American Arms was a trade name used by the H&D Folsom Company of New York on firearms they retailed circa 1900. It could have been manufactured by any of a dozen makers, but most likely by Crescent Firearms. Like any other 100-year-old tool or machine, parts are where you find them. You may be able to get parts that fit (or can be made to fit) from a local gunsmith or at a gunshow, but no one will have a catalog of parts for it.
try numrich gun parts
Try gun shows, Shotgun News, Gun List, local gun shops.
numrich gunparts.com has everything but the stock
One can get spare parts for a Nikko shotgun at some local gun retailers or through gun manufacturers. Gun parts can also be found through gun classifieds and gun auctions.
Try e-gunparts.com
Your gun is a Mossberg 500 with a Wards name. If you can't get parts from a local gunsmith, try Numrich Gunparts
Pretty much an impossible undertaking.
Try want ads, e-gunparts.com, gun shops, gun shows, Shotgun News
Try e-gunparts.com, gun shows, gun shops, Shotgun News.
Try Numrich gun parts corp.or gun broker.com under shotgun parts.
numrich gun parts
Gun shop, gun show, want ad, internet.