I would start with numrich arms,they have an awful lot of old gun parts.
Probably at Savage customer service website (Savage bought Stevens in 1920)
Numrich Arms should have them.
Get a copy of the Gun Digest Shotgun Assembly/Disassembly manual. It should have the Mod 67.
The owner's manual, configuration and comparison with known examples.
You can find what you need at webdept@gunpartscorp.com .
If the owner's manual doesn't have instructions, seek out a qualified gun smith.
www.savageparts.com has a schematic. I advise against disassembly unless you absolutely have to. sales@countrygunsmith.net
Follow the instructions in the owner's manual. If you don't have one, find a gunsmith/gun store.
This can be found on the manufacturer's website. You can also find one when you purchase the gun at the store.
To locate a manual for your shotgun,you must provide the model number for your shotgun first.All shotguns made for Montgomery Wards(Western Field) were made by other firearms manufactures for Montgomery Wards to include Savage,Stevens,Mossberg,Noble and more.
To disassemble a Stevens Model 59B shotgun, first ensure it is unloaded. Then, remove the forend by unscrewing the forend nut. Next, push out the trigger plate pin and remove the trigger plate assembly. Finally, push out the hammer pin and remove the hammer assembly to fully disassemble the shotgun for cleaning or maintenance. Remember to follow all safety precautions and consult the manufacturer's manual for detailed instructions.
john