You will have to be more specific. Major assembiles, all parts?
Go to a gun shop
gun shows, gun shops, want ads
You can try e-gunparts.com and gun shows.
Want ads, e-gunparts.com, gun shop, gun show.
you can find parts for your Stevens at bob`s gun parts .com
Numrich gun parts, look under Marlin/Glenfield parts list
I would start with the numrich gun parts corp.They can be found on the web.
the 12 guage is a caliber not a gun
Try gun shops, want ads, e-gunparts.com, gun show.
Depdends on weight of gun, caliber, load and velocity of projectile
You will need to identify the gun better than a "model 170" as in what is the manufacturer, caliber, type of gun, etc. Parts are available here: Numrich gunpartscorp.com Jack First jackfirstgun.com Bob's Gun Shop gun-parts.com