We have them. gunshop@nctv.com
I have parts for that model. sales@countrygunsmith.net
Proofhouse.com has a store brand cross reference chart that might help you.
I believe that your Sears shotgun is a Winchester model 37A shotgun that was made for Sears Roebuck And Co,.
http://www.histandard.info/PDF/Sears%20Shotguns.pdf
Winchester
sears roebuck and company
Its a Sears branded Mossberg 500.
The value of a Sears and Roebuck 12 gauge shotgun model number 281512651 depends on its condition. This gun in excellent condition is valued between 100.00 and 135.00 as of 2014.
There was one at an on-line auction but it was a 12ga. It went for $160. It was Aumann's auction or something like that.
1952 by High Standard for sears& Roebuck
Winchester 1200
$49.95