Diamond Arms Co was a trade name used by Shapleigh Hardware Company of St. Louis, Missouri in the late 19th and early 20th century. It may have actually been manufactured by Iver Johnson, J. Stevens, or one of several Belgian firms. Parts will be hard to find. If you can identify it as a particular IJ or JS, Numrich Gunparts can probably supply them. Otherwise, carry it to all the gunshows within a hundred miles and dig through bins of misc parts.
I can certainly understand wanting to put Grandad's Old Gun back in working condition, but since these store-brand shotguns are not high-dollar collectables and seldom used as shooters, their value (other than sentimental value) is as a decoration. The cost of restoration or repair will probably exceed the gun's cash value.
Go to gunparts.com "Numrich" they have new & used parts
it is a Stevens, parts are interchangeable...
Buy my 20 g companion,and there are your parts?wjw2010@live.com
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
A FEW parts are available from gunpartscorp website.
Depending on which parts, they may need to be made.
Numrich Arms should have them.
Follow the link to the related question.
The 238 is similar to the 258. For parts, try gunpartscorp.com
i found a small list of parts at numrich guns and parts
Some models of Diamond Arms were made by the Crescent Fire Arms Company for the Shapleigh Hardware Company of St, Louis, Mo. between 1982 and about 1922.
Diamond Arms shotguns were made by several manufacturers, but if the rest of the patent date is '13', this one was by J. Stevens Arms and retailed by Shapleigh Hardware.