This is the link for WES. I imagine that if you got in touch with them, maybe they have a forum too, someone will be able to give you some names to start with.
Good Luck.
ps, I don't know about the prevalence in the UK, but just check that if there is Impressive in the horses' lines that it is HYPP tested. I won't touch a registered horse that isn't N/N.
I'll go and find the link just in case you have no idea what I am babbling on about, if you do, apologies for telling you what you already know. http://www.vgl.ucdavis.edu/services/hypp.php
I went on a experience western thing at The Mendip stud last year. They have some fantastic horses and staff. Met all their stallions too and they all had fantastic temps. They import a few too http://www.themendipstud.com/
Hi! lots of places to buy a QH, although it depends just what you are looking for. We have QH's, all bought from different breeders here in the UK. We've tended to buy weanlings although older, trained horses are also for sale. People also import from the US, Germany, Italy and France etc. A friend of ours has just bought a lovely gelding that had been bred and trained in Germany, before being imported and ridden for a few years, and then sold on. Have a look at the AQHA.UK site, as that is the first place people will put their QH's for sale. And please feel free to PM me if you would like any info, or breeder recommendations.