I think that you'll find oolong tea hard to find in the shops. I've never seen it in supermarkets. Also, it doesn't appear on the Holland & Barrett website, so it's probably unlikely that you'll find it in health food shops.
This website suggests that, unless you happen to live in London, Glasgow or Edinburgh, the only place you'll be likely to find it will be in specialist Chinese markets:
http://fergusmurray.members.beeb.net/oolong.ht m
Otherwise you might be forced to shop online. That website recommends an online supplier in Edinburgh. They quote prices between �2.85 and �4.60 for 50g of Chinese oolong. (Formosa oolong is slightly cheaper at �2.48 but it's currently shown as out of stock).
I'm sorry that this response doesn't fully answer your question but I hope that it will be of some help to you.
Chris