I believe wholesale tropicals in London do mail order too. I've not used them for that, as they are my lfs and have a fab range of fish. Though they don't stock a vast range of shrimp unfortunately. They have some amano @ £2.50 each but they are usually quite small. They might be able to order in for you if you ring them up though.
I know of no others unfortunately - apart from some scouting on eBay and checking out feedback before buying anything.