You *might* find an aftermarket stock for your Hi-Standard, but my guess would be a pistol grip is the only ones out there. If I were you I'd put a recoil pad on the existing wood stack and call it a day.
Great idea, except HS stocks are impossible to find or available for crazy money. Moss & Rem are a dime a dozen so it woudl be great to learn than either would be work or could be modified easily.
Here is the link for a cross reference guide between store brands (sears, JC Penny, Kmart etc) and the real makers. Sometimes you can find a stock cheap because it's a sears...but it may fit a flite king!
As to fitting other brands, that depends on how close the design is and on how much use of epoxy is acceptable.
If you're willing to basically rebuild and refit a stock, you can make something up that will work.