The information I have is from E Strack's great book, "Pearls".
Bangladesh has been the source of both fresh and salt water pearls in the past. There was some action in the 1990's when in 1994 some Bangladeshi natural freshwater pearls were offered at the gem show in Tucson. It turned out later they were offered in Germany as Pakastani Freshwaters. So Strack does not know for sure what they may have been.
Aside from the dubious freshwaters -which were very tiny, but highly metallic in the photo in the book, there are a few desparados who still comb the great Bengal Pearl banks for natural seawater pearls. It is not very profitable even though it has not died out entirely.
In other words, any pearl farming going on in Bangladesh has originated since "Pearls"was published in 2001- English edition in 2006. Therefore my guess is that Bangladesh sells Chinese freshwaters to tourists as being from Bangladesh. This practice is well know in tourist traps all over the known world. Filipinos sell them as Filipino pearls, Bali as Balinese pearls Arabians as Arabian pearls, you name the place, there will be folks selling Chinese freshwater pearls as native pearls from the region. The countries I just mentioned all have recent reports in this forum for doing just that.
I am always sorry to be the one to tell people there is no such person as Santa Claus or that Chinese freshwater pearls are not native natural pearls.....
Please let me know if you have actually seen the farms, because I don't know of any big retailer who buys from Bangladesh. I will happily eat crow if there are.