Buy parts for 410 Stevens model 67 pump shot gun.
Try e-gunparts.com
I have parts for that model. sales@countrygunsmith.net
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
I had to buy a gun to break. Don't have it now. I do have a parts list from Stevens i.e. exploded diagram. Not much use unless you can source a second hand gun or part.
www.gunstockinc.com
it is a Stevens, parts are interchangeable...
Have you tried e-gunparts.com?
Riverside was manufactured by Stevens, so if you can identify the equivalent Stevens model, you should be able to find parts. Check with a local gunsmith.
Check on Numrich gun parts corp website.
Numrich Arms has parts for the 311
Start your search at Numrich gun parts corp.They can be found on the web.