You might be a touch late at your local garden centre - but they might still have some.
I put my Garlic in the week before Christmas - I ordered a mixed pack from these people
http://www.thegarlicfarm.co.uk/shopgarlic.asp? catid=7&cat=Planting+Garlic+Order+Now&pcatid=1
That might be a bit much for you - it was enough for just over a raised bed 3m x1.5
But you can order individually
Mind you the Elephant Garlic has to be seen to be believed looks like they're out of stock for this year but each clove was about the size of a table tennis ball