Yes, thistle is a common name of edible plants (herb) that fall into the Asteraceae family. I have a photo of Milk Thistle in my gallery on page 2. Globe Thistle or Scottish Thistle is quite eye catching and on my shopping list for next Spring. They would look great with my purple coneflowers. It also goes by the name Echinops.

The true Scotch thistle (Onocordum acanthum) can be grown easily from seed which is available on line, but be aware that it makes a very tall plant and can reach a good six feet.
The other British thistle are in the family Carlina and in a pot you might like the stemless C. acaule which has quite a large flower head but only reaches about 20cm.
If you look at a good wildflower book you can see all the others - 14 of them! I don't think you'd be able to buy them - never heard of anyone growing them n the garden!
The Echinops that Bathgate suggested would be a lot easier to grow and looks a lot like a thistle but it wouldn't convince a Scot...

If you want a thistle as a centrepiece, then I would suggest Cynara cardunculus (globe artichoke). This, I believe would certainly make a statement in a pot as it looks like a giant thistle.

If you haven't made your pot yet, be sure to put a drainage hole in the bottom, unless you're planning on using an ordinary pot inside it.