There should be a phone number in the owners manual that came with your shotgun to where you can buy parts chokes etc. If you don't have the owners manual you can easily obtain one from Remingtons web site.
I have parts for that model. sales@countrygunsmith.net
There is a ammo clip for a J C Higgins shotgun model 58324 16 gauge. You can buy it as a replacement part.
You would have to list the model number of your shotgun,to identify the maker of your sears and roebuck shotgun,in order to get the correct buttstock.
Try your local gunsmith. The Riverside is a Stevens shotgun. If you can find out which model it is, you can probably find the wood at Numrich Gunparts
Try e-gunparts.com
Try e-gunparts.com, Shotgun News, Gun List.
where can i buy parts Kmart
You can buy on ebay.
I have parts for that model. sales@countrygunsmith.net
Buy parts for 410 Stevens model 67 pump shot gun.
berry38