Yup, what ironwood said, e-bay. Most are listed under "black powder". He provided the link for searching.
People will strip all the furniture off a stock and sell the individual components. The one Ironwood has linked is a Renegade Hunter with a single trigger. But if you watch for just a few weeks you'll see the standard stocks go for 50-100 with about 15 for shipping.
Advise; Buy another stock for yourself, all your parts will transfer hassel free, then list yours for 10 days with a specific statement "inlet for 57 sml" and you'll find a buyer for very likley the cost you have in the new stock. You can start with a minimum bid.
At one time I wanted to put a 57 on a Renegade, but I just couldn't bring myself to cutting the wood, once you do your stuck with it. I'm sure the are a BUNCH of folks out there that have the same idea, and would rather have another stock.
I'm curious,haveing had both the 57 and the T/C peep in my hand ( the 57 being a much better sight).
What is it you don't like?