It is a Stevens gun, general utility type shotgun. Value around $200 in good condition. sales@countrygunsmith.net
Depends on what is marked on the gun.
Try Numrich arms @ www.e-gunparts.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
You will have to carefully note exactly how the gun is marked, first.
Riverside was an 'economy' brand used by the Stevens division of Savage in the 20's and 30's.
Eastern Arms was a brand name sold by Sears Roebuck. The Model 1929 suggests that it was made by J. Stevens Arms Co.
Try googling it. I believe you will be surprised.
It is a Stevens shotgun, based on a Browning patent. Inexpensive.
Sorry- that is a serial number, and conveys no information. If the barrel is not marked, you need to take it to a gunsmith who will measure the chamber- not only for gauge, but for the correct shell length. Just because an unfired shell fits does not mean it is the correct shell. And it is not a rifle, but a shotgun.
Would need to know exactly how that gun is marked.
No. Riverside was bought by Stevens in the early 20th Century and became one of their house brands for a while before being discontinued. However, spare parts are available for most Riverside marked guns.
A SxS in useable but not like-new condition will bring between $100 and $250. A 20 gauge or .410 will be in the mid to upper part of that range and a 12 or 16 gauge in the lower to middle part.