Guillermo, if you read that old thread, you will see that there were two routes to an aftermarket 3" Python.
Colt sold off excess barrels, I remember seeing them advertised by Numrich. That was 10-15 years ago, they are long gone by now, undoubtedly put on guns and sold at fraudulently inflated prices.
One distributor made them up by sawing off the ugly 8" guns.