Alot of tiliapia from these places are hard to get in general, mostly becuase it is banned to take them from their natural habitats now due to overfishing, already low numbers and competition with other fish.
Check your exotics laws. The U.S. is not the only place where lots of these species are banned. Australia has strict regulations on exotic species as well as do other countries.
Tilapia, in general, are just hard to find because of the stigma of them being nuisance fish that outcompete and displace natives.