They grow from rhizomes. Have a look at Claire Austins website.
http://www.claireaustin-hardyplants.co.uk/catalogues.php
But they are usually on sale from the beginning of June onwards, tailing off as they finish flowering.

ok thankyou I will have a look :)

I saw a couple of rather sorry looking Iris for sale in Dobbies the other day in the 'bargain bin', maybe worth having a wee look now Kate.

I dont know were in the west mids you are, but i have irises that need dividing and if you are anywere near, say merry hill, i could let you have some

thanks Scottish we have one near us...wow Jenfren Im near Wednesfield :) thanks for your comments everyone :0

Have split up large clumps and have about 15 potted up in the greenhouse, could meet at merry hill & give you some if you want. I shall be there next week not sure yet what day.You could p.m. me if interested