The problem isn't nessecarily the shop, it's the attitude to fishkeeping in general, which is something that is unlikely to change.
Most branches I've been to seem to do a fairly good job with what they're given- as far as I'm aware, like most shops they don't have QT facilities so if fish come in ill, it's tough luck. And being on a centralised filter system doesn't help, but again, that's pretty much tough luck. Fish stocked? Well, I've never seen a shop that doesn't stock common plecs, silver sharks and the like, and I haven't enquired but I bet most of those would probably sell to an undersized tank. I know our local branch occasionally gets some quite decent things in- I've seen microrasboras, american flag fish, dwarf chain loaches- it would be nice to see more 'practical' fish, but as shown by this thread, the people who generally want such fish don't shop there. Joe Public usually wants- and therefore buys- neons, guppies, plecs, danios, angels and such.