well, the Indian yarelli are seasonal, they can catch them only at the beginning of the rainy season, when water is not too high, too low, or weather too hot. last year they caught some for me, and the weather was over 100 degrees, so traveling the hundreds of miles back to Calcutta for shipping was not possible, well they all died. They also don't have the luxury of nice fish trucks with airconditioning and chiller equipment either.
as for the thailand ones, they come mixed, sometimes with bagarius rutilus, and sometimes all bagarius bagarius. Not sure about the habitat they come from, they tend to be a little less active than the Indian ones, even that I only know of a couple of exporters that get them.