Welcome to the forum,
Anything is possible and if you can think of it; it probably has been done. As for the 9mm in the 38 (moel 10), the 9mm is a .355 bullet and the 38 is a .358 bullet so accuacy would suffer. Ruger made the blackhawk in that combo but the 9mm was never that great out of it either. The 9mm has more of a jump to get from the case to the forcing cone too so that is not going to help with your groups. I would say by the time you spend the time and money on the cylinder, I bet you would be disapointed with the results. The 9mm would also be a snappy round for the gun, many folks have not shot a 9mm revolver and most of the time those that do are surprised of the recoil and muzzle rise. I have the SP 101 Rugers in 357 and 9mm and the 9 is a handful campared to hot 38s and mid-range 357s. Keep the 10 as is and seek out someone that has a 9mm revolver and shoot it for a while. I would not go down the road of buying another 9mm revolver unless the price is to die for. Happy shooting.