I looked for my Gun Parts Catalog last night (they have the breakdown drawing on many rifle/shotguns in there) - of course I could NOT find it

Like I said - Give Gun Parts Corp a call - I would not be surprised if the had every part of that shotgun in stock - in the days when they used to have a storefront, it was always fun to drop by - they had buildings and buildings of gun parts (at least 5-6 good sized buildings). At one time, Numrich arms owned AutoOrdinace Corp - yep, the Thompson MG folks