First. welcome to the forum- glad you found your way here.
Stevens was a venerable company- founded in 1864, creator of the .22 LR cartridge, bought by Savage in 1920, operated as a subsidiary of Savage until they folded the name in 1950. Made a bit of everything including machine guns for the US military.
Photos will help. If your gun IS a 235, parts will be a matter of luck, dedication, and ingenuity. Gunpartscorp.com has a partial illustration for the 235, that shows the firing pin and buttplate- but sold out. A true gunsmith can use the existing firing pin to machine a replacement for the missing one.
Maybe I can narrow down the date of birth a bit- the 235 was made from 1912-1915, ALL shotgun making stopped 1916, resumed 1920, and the model 235 ended production in 1932. The "Arms & Tool" name was not used after 1915, so you have somewhere between 1912-1915.