Hi, Colddragoon.
Charter Arms used to be the parts supplier in the USA. They are still listed on Chaparral (Italy) website, but I don't believe Charter is handling the Chappie or parts any longer. Charles Daley is also listed, so you might try them. Let us know how it works out. Last report I had was that NO one on this side of the pond had parts.
http://www.chaparralarms.com/index.htmIf neither of them can help, you may be able to get parts from Italy. They have a contact number.
The Chaparral parts and original Winchester parts are supposed to be interchangeable, so you might be able to use a replacement from one of these guys.
http://www.chasjonesgunparts.com/page/page/498048.htmhttp://www.winchesterbob.com/index.htmI see original parts on ebay pretty regular, as some folks part out the old rifles from time to time.
If all else fails, pick up an Uberti 76 part from VTI and see if it can be fit. Worth a try!
Good luck, Amigo!