You will have to try e-gunparts.com, gunshops, gunshows and want ads.
Your shotgun is a Mossbeg 500. made by them for Sears. Go to the Mossberg website, customer serivce, owners manual, and download the manual for your shotgun.
http://www.histandard.info/manuals/sears/pashotguns/index.html
need a diagram of sears model 66m shotgun for takedown
your sears shotgun was made by savage arms.There model number was savage model 96.
Manuals for the model 101.5380D shotgun may be found at some Sears Roebuck gun dealers. However as an older gun model manuals may need to be special ordered by the store.
http://www.histandard.info/manuals/sears/pashotguns/index.html
What model????
Yes, you can remove the barrel of a model 66 Shotgun!
price for sears 12 ga.model 101.7
The manual can be downloaded here: http://www.histandard.info/manuals/sears/index.html
You can get it here:http://www.sears.com/en_us/customer-service/product-information/find-a-manual.html
I believe that your Sears shotgun is a Winchester model 37A shotgun that was made for Sears Roebuck And Co,.