If you know the make and model, you might be able to find the parts at Numrich Gunparts. But it would probably be easier to look in the yellow pages for a gunsmith.
Depends on the model. We usually have parts.
Part #39-279, but I also am out of stock at the moment. I get them regularly, however, as I get parts guns in. sales@countrygunsmith.net
gunbroker.com
Try www.gunpartscorp.com
Numrich Arms. www.e-gunparts.com
You can find most of the parts at e-gunparts, to find them do a google search of "e-gunparts".
Numrich gun parts
Modle 101 1380 410 shotgun
try gunbroker.com they might have parts
Trry Numrich or e-gunpartscorp.com
www.e-gunparts.com
Numrich (Gun Parts Copr.) has some Iver Johnson parts.