Not from Bristol but near Bath. I have only bought fish from the Aquatic Habitat in Brockworth, Glos otherwise they have come from forum members.
Maidenhead Aquatics North Swindon is quite good as are Blooms (1st Swindon exit). Parkers at Yate also. Are you looking for anything in particular?
Agree (mostly ) with Cheffi apart from Parkers, didn't think much of it, what ever you do give Cadbury garden centre a miss, awful tanks full of bad looking fish poor things.
Unfortunately Bristol's not very good for LFS's, I ethier travel to Glous or Swindon, Tri-mar aren't to bad for fish though they've a good choice and not bad prices, and saves travelling.