I'm pretty sure that almost all of their fish come from American farms, which is pretty cool. this also means that the fish are already acclimated to our tap water.I haven't been in a Petco for some time, but some of the fish I currently keep are Petsmart purchases. Some 5yr/old silver hatchets for example, one 3yr/old female "sunburst' platy and a couple of fat tiger barbs. A couple of blue female bettas too.
Last time I saw them unloading fish, the boxes were from Segrest Farms out of FL, just like the every other store uses in my area.
you should have a QT tank anyway, so just get some 6/$6 platies and save the specialty shops for fish that are delicate, unique, or that you may need to have a specific order for.