A friend has bought a riding pony from here http://www.properhorses.com/ and he was exactly as described. What are you looking to buy, if it's youngstock, you could contact henryhorn on here, she has a few for sale, I think various ages, mostly by the lovely Chocx.
Hi there: if you would PM me or e-mail I might be able to help, based on my rather limited experiences when I was looking a few years ago. There is one dealer you definately should avoid who used to trade in the South Devon area but they're now trading as something else. I don't think its proper to name names in this forum - so feel free to PM me OK.
I don't know of any good ones in the area, but I know of one which should also be avoided, also in the South Devon area, so possibly the same as above..............