Monsterfish keepers are not really the norm and so most LFS's will be catering for a market where smaller tanks are more common. So we have tetras, gouramis, guppies, swordtails, mollies etc etc. However, the classic three fish which they always sell though, and indeed to these people with small tanks, are plecos, oscars and bala sharks, all cute and tiny, but we know better and we could have a seperate thread to discuss the rights and wrongs of that.
My LFS is no different and so if I want something a bit more oddball or chunkier I just ask him. He's basically told me he can get me whatever I want, unless it's banned, and not many are banned in the UK because they haven't got a cat in hells chance of surviving the cold if someone was so stupid to release something into the wild.
He got me a flagtail a couple of years ago which he's never stocked before and when I quizzed him about frontosa he just told me to give him a shout when I want a group.
So before having to go down the route of ordering online and all the potential grief that can entail, i'd just ask at your local LFS. If they're half decent they should be able to help you, and even better, if you do live in a warmer climate they should also be able to tell you if the fish is legal in your area and offer you advice on keeping said fish etc etc.