First, some general info:
The company name was the J. Stevens Arms & Tool Co. up until WW-I. At that time their factories were taken over by New England Westinghouse for war production. After the Great War, Savage acquired the factories in Chicopee Fall, Mass., and set up the J. Stevens Arms Co. a wholy owned subsidiary of Savage Arms Corp. In addition to Stevens firearms thesr factories turned out a lower priced line of guns under the Riverside Arms Co. name up to about 1930 and the Springfield Arms Co. from 1930 to WW-II.
You can begin to date your gun based on the way the Stevens company name is written:
J. Stevens and Company 1867-1886.
J Stevens A&T Co. or
J. Stevens Arms and Tool Company, 1886-1915.
- no guns produced 1915-1920
J. Stevens Arms Company 1920-c.1940.
Stevens c. 1940-1991. AND 1999+
if both the Stevens AND Savage names appear, post 1948.
After 1948, all Stevens and Savage guns carried a date code stamped onto the gun. The date code stamp is a circle or oval containing a letter and a number. The letter coorespondes to the year of manufacture using the following translation. A is 1949. B is 1950 and so on through X. This code can be found almost anywhere on the gun and sometimes requires removing the stock to find it.
Also, later ones share a common platform with Savage Arms.
That said, you can find parts for Savage/Stevens/Springfield/Fox here:
Scroll down to almost the bottom for the shotgun parts.