I'm pretty sure that some wholesalers require you to have an employer indentification number(EIN) or something similar. I've been to non fish related wholesaler sites before that asked for the number before they would send you their prices. I've bought from a wholesaler before, who didn't require this, so it might not always be the case.
As others said, you generally have to buy in bulk.
If you are serious about this, you should start by reading some small business books from your local library.
I wan't to start a pet shop as we'll i would sell the good stuff not just tetras and i would be one of the few responsible pet store owners i wouldn't carry fish like pacus TSNs RTCs or pimas but i would speacial order them for certain people i know that can care for them you should do the same
Alot of pet shops order fish from the same places we do we'll atleast the good ones places like petsmart order from bulk sellers which can in some cases be good