Provided you add enough humus rich material the worms will come of their own accord. Adding worms before the soil is suitable for them to live in simply means they will either migrate or die.

Glad you forked your ground over as this will help a lot as your bed is not very deep and now things with deeper roots will be able to push down into the original soil. (I'm assuming you did this after you took the photo! Agree, worms will come when you add manure , composted greens etc. Be patient, there is no need to buy any.
Lots of worms in your garden is a sign of lots of good humus in the soil as this is what they feed on.

My parents were keen fishermen. I remember every day my mother emptying the teapot onto the same spot on the garden to encourage worms at that place. Then when they were going fishing she used to dig up a whole heap of them to put in their bait box.
If you have access to a canteen or OAP club, they would probably save the tea bags if you take them a container with your name on . Those big tea pots
need 8 tea bags to serve tea to 40 people.
Dont know about coffee, never drink it.

jimbob what you are putting in the beds ,will be enough to encourage worms if you were to leave a small pile of manure in one spot on the ground you will after not many weeks lots of worms so the same will happen in your beds no need to go buying them

Couple of thoughts here, and apologies if I come across bossy or knowitall...
From the photos, it seems that at least two sides of the garden are bounded by house/road. Is the fenced side against a neighbouring garden or a street? I ask because you're not likely to have worms visiting your garden from the house side, or from the road side...
You may not have as few worms as you think, if your weather has been cold recently, as they do hunker down deeper for winter. But if they aren't going to migrate in vast numbers from next door, you would be best off getting several inches of rotted manure into the bed asap, so that even if you don't plant veggies this year you can at least grow worms.
My experience mirrors Snoop, manure-wise: if you buy it, they will come! They can breed well in the bagged stuff anyway, so if you were to put in a layer say 4-6"thick of manure this month, the wormlings can be getting on with breeding while you're doing other stuff.
Whatever you put in the raised beds will flatten and reduce in volume much faster than you'd want, so you're not at risk of it being over-manurey!
Also, come March or April, you can start to use the bed for non-veggie stuff - I'm thinking maybe set up a couple of cane wigwams and plant sweet peas, takes no time and allows you to envisage whether to grow runner beans next year, where the shade would be cast so what you could plan to grow underneath...

Another thought: some root veg don't like manure that's too fresh, so perhaps use a massive load of it this winter so that in a year, when you're really ready to get growing, it's all well incorporated and not as rich.

Provided your raised bed is on open soil at the bottom, you don't need to buy in any worms - they'll come on their own. Adding humus rich materials, as already advised by others, and which you seem to have already done, will encourage them, and as Teadrinker says, worms go down much deeper in winter anyway, so that would explain why you didn't find any/many.

I have never found any worms in my sub-standard clay soil thats why I advocate the tea bags method. Cheeeeeeeep!

When we took over part of a neighbour's garden to grow veggies on the soil was totally devoid of worms… Less than a year later they were there in plenty as we had built up the humus level. Diane how do you grow anything without worms?

Teadrinker, giving great advice isn't either bossy of knowitall!

Jimbob carrots don't like newly manured soil, if that's any help.

I was digging holes to sink my new pergola into at the weekend - 2ft deep and it wasn't until I was very near the bottom until I was seeing worms. Mrs Robin had a field day when I was finished :)

Thanks everyone for the informative answers, once again last night I new nothing about worms and through the power of growsonyou.com I feel I know enough to make the decision that I'm not going to buy worms. I feel now this statement is true:

"If you create the right environment / habitat for the worms they will come on the own accord"

Teadrinker - the fence is against a neighbour's house, however we live on a new housing development so the soil will be of the same quality. Also please do not apologise for being knowledgable on a subject that as last night I knew nothing about. I'm interested now in the sweat pea and cane wigwam idea for this year. What time of the year would I need to think about constructing and planting this arrangement?

There are many methods of sowing sweet peas. Some people sow their sweet pea seed in autumn and some in spring. Monty Don did an experiment with both. I can't remember which side he came down on though! I usually sow mine in small but deep flowerpots in spring, just a few to a pot, and keep them in the back porch until big enough to plant round a wigwam. You do need to take action against slugs or they will scoff the lot!

Even here in the desert, worms will appear when there is enough organic matter. If you want to hurry it along a bit, come spring, buy some red wrigglers from the local fishing supply.

For the purpose of just trial-running the bed, I don't know that I'd even start the sweet peas in pots. I do, just out of habit, leave sweet pea seeds in a mug of warm water overnight before sowing, although latest advice suggests there is no benefit to doing it!
So in late March or anywhen in April, set up a wigwam of 6foot canes, or longer if you don't mind spending a bit more. Just poke 2 seeds into the soil, 2 inches deep, at the base of each cane. Whole project, 10 minutes.
If your other commitments will allow you to spend a bit more time and/or money, you can buy pea-netting which a very flexible fine mesh, and you attach it to the cane wigwam to form a cone. This then gives the plants an easier way of climbing, which they do by wrapping their leaf stalks around whatever they touch against. So, a better, faster, smarter-looking effect. But then in the autumn you have to pick all the dead plant material off the net, before putting the net away neatly for next year and composting the plants. I'd just personally try to get the peas to climb the naked canes.
Keeping an eye out for slugs on seedlings and young plants is always worthwhile, also try to keep pigeons off them too. But since your garden has been such a blank canvas you may not have too many slugs lurking around yet. I've got spares if you need some...
And thanks for encouraging me to waffle on.