You could try looking to a custom stock by Bullberry or VVCG, I have seen several thumbhole styles on Ebay. Depends on what you wnat to spend. The pictures I have seen of some stocks from both BB and VVCG are just downright too good looking to take outdoors. But they are laminates and should be quite tough. The cheap way out would be to get a lace on cheekpiece, or even cheaper yet, tape on a rag or towel.