Sears 200 series = Winchester 1200. Parts should be available from e-gunparts.com if you can't find them locally.
Typical Crescent single-barrel shotgun. I have a good supply of parts. firstname.lastname@example.org
My cross reference list indicates that this is a Savage 59. If your local gunsmith can't find the parts, you can check with www.e-gunparts.com
Parts for these shotguns are hard to find. EAA Corp carries parts for Baikal shotguns. A good gunsmith might also be able to help make some parts.
You could try Gun Parts Corporation.
You can't... you will have to make them yourself or have a machine shop make the parts
Some of the larger used parts dealers may have a small quantity. Try www.e-gunparts.com or Jack First Gun Shop.
These single-barrel Crescent shotguns range from < $50 as a parts gun, to maybe $100 if in excellent shape.
Need more info. Which manufacturer & which model??