I would try the numrich gun parts corp.They can be found on the web.
On line auctions, gun shops, gun shows, pawn shops.
I have a complete 90% Crescent 12 ga 100,00 yours..
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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.
The wooden forearm is easily made, but if you need the metal part of the forend you are in for a tough time. We are one of the largest used parts dealers in the country and have not had a Crescent .410 forend iron in years. sales@countrygunsmith.net
Typical Crescent single-barrel shotgun. I have a good supply of parts. sales@countrygunsmith.net
The only Crescent shotgun that I know of that was nickeled was the 20 guage, 14 inch barreled Knickerbocker. A shotgun with a barrel length of 18" or less requires a Class C license from the federal Bureau of Alcohol, Tobacco & Firearms. Assuming you are correct and it is a 12 guage, it was originally blued and parts should be available from http://www.gunpartscorp.com.
Some Enders Royal Service shotguns are Crescent Model 60's marked with Shapleigh Hardware's trade name, but some were made by other manufacturers.
I have parts for that model. sales@countrygunsmith.net
Actually manufactured by Crescent Firearms. Parts might be found by checking some of the major used parts dealers.
Highly unlikely you will find any. Getting them made will probably cost more than the shotgun is worth.
I have a Marlin Firearms Co. 12 gage, bolt action shotgun.