Can't find any local to you, but I had a look round and found these:
http://www.skianmhor.co.uk/
and
http://www.lrpstore.co.uk/contents.asp.
The second one is quite annoying - I really needed some elf ears for the missus, but didn't know the place existed (and it's just a few miles away). It doesn't appear to be a very cheap hobby, though. It might be worth doing a search on "elf" or "eleven" costume, because when I was looking for a way to make elf ears, I came across a few sites that gave you budget ideas on how to get a cossie together (then you could just order a set of ears). Sorry, but the bookmarks are long gone from my system.