i have a few myself, they are only imported by a few people around, I'm one of them. When they're offered that's when they're available, once they're gone, they're gone. Most of the other masheers you see on the market are not Indian ones, but from Malaysia and Thailand region.
I've talked about importing fish from India, most people just want the rare stuff, and the rest of the bread and butter, get stuck....of course, nobody wants to pay $500 for a masheer either, so from an economical stand point, its not lucrative or feasible. Might be fun...but that's about it, that's probably one of the reasons why all these years in the hobby you rarely see or hear about masheers.