So... first off, I do like how getting the materials for recasting R9/Nirvana requires some effort to obtain and isn't just outright buyable, but getting the mold for the weapons can get a little frustrating due to the low chance of getting the one you want on top of the time and effort needed to kill Vile: The Incacerate.
So here's my suggestion: every time you kill Vile: The Incacerate, the quest not only awards you a Basic Badge, but also a Weapons Badge. A certain amount of these ''weapon badges'' (maybe along with a certain amount of coins) could be traded for a weapon mold of your choice at the forges.
Since the chance of getting your desired mold is 1 in 31 (there are 21 Nirvana molds and 10 R9 molds) the amount could be 31 Weapon Badges. If you get your weapon mold before those 31 runs; congratulations, you've got above average luck. If not? No problem, you can get the mold with the badges you collected.