I am late to the party on this one. Awesome mods everyone.
The M93 Stock was offered on a few early Hot Toys USMC figures as mentioned. One was the MEF II (Wesley Snipes headsculpt, in desert tan flight suit, also came with the Ltd Ed SOCOM 16 rifle) figure with the camo painted M4 and Simunition gear, and I think another earlier Marine in both green and desert camo options as well.
Dr.Figures (the kings of recast) copied the HT stocks out of both cheap plastic, and resin on their rifles, and they suffered from some molding issues, and details were lost. They did them in both black and tan versions. And the paint apps were awful too. But they were a way cheaper alternative than hunting down a hard to find(think more expensive) Hot Toys rifle and cutting it up for parts. I imagine the shop that carried a lot of the brand is still kicking around. I’ll see if I can find some of the Dr.Figures versions, as I scored them on auction on Ebay super cheap a long time go.
These stocks were also from the time when the early HT rifles were bigger than they should have been scale wise, which will now translate into a stock that is probably a big too big to swap onto current manufactured set rifles to look accurate.