If you're looking for a real one????????????
If you're handy and a good replica will do, I've done this in the past.
Take a bubbaed butt stock, which can usually be had for the asking at a local gun shop or $5 at most and cut the top off, Scrape/sand off everything that doesn't look like a cheek piece. Drill some appropriate holes and finish with BLO. The first one you do will take a couple of hours. After that maybe an hour. Just be careful and they are almost indistinguishable from the real thing.
No, I don't do them for anyone else.
Give it a go. If you're like most of us presently, you have lots of time on your hands.