numrich gunparts.com has everything but the stock
Pretty much an impossible undertaking.
Parts for an American Gun Company shotgun will only be found as part of another shotgun. Haunt the local gunshows for one that is being parted-out. As for the gauge (not caliber), did you mean "bigger than a 410"? There have been 24, 28, and 32 gauge shotguns made. Of these, only the 28 is still available in the US, but I believe 32 gauge shells may still be commercially loaded in Europe.
numrich
http://www.e-gunparts.com
delolosi
You can purchase parts for a Ranger model 30 16 gauge shotgun at these locations. Gunbroker, Topgunsupply, Budsgunshop, Gunpartshop and Midwayusa.
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There are some sources for Crescent shotgun parts, but it is very possible that parts will have to be repaired/made.
Check the yellow pages for gunsmiths or go to a local gunshow. Be prepared to spend about twice the value of the repaired gun. Numrich Arms @ www.e-gunparts.com
DO NOT ATTEMPT TO USE PARTS THAT WERE NOT MADE FOR YOUR WEAPON!!!!!!!!!!! Danger, danger, danger.
Numrich firearm parts. See link below.
I have parts for that model. sales@countrygunsmith.net