Try e-gunparts.com, gun show, gun shop, want ads.
I have parts for that model. sales@countrygunsmith.net
The 238 is similar to the 258. For parts, try gunpartscorp.com
You might find what you need at webdept@gunpartscorp.com .
try looking at savage or Stevens shotgun diagrams. I found a firing pin for a 16 gauge riverside it was an old model 94 Stevens part
Stevens made jc Higgins shotguns ,the model 311 interchanges with the jc Higgins
Try Gun Parts Corp. They have parts for nearly every gun ever made.
Try Numrich or Bob's Gun Parts. They are both on the web.
Numrich has a gun parts website. Best bet for any gun parts or schematics...
www.gunstockinc.com
Buy parts for 410 Stevens model 67 pump shot gun.
I have this model gun however i know very little about it. EBAY e-gunparts.com is an awesome parts site
It's a pretty common gun, so any gunsmith should have a source for parts.