Try the internet, gun show, gun shops, want ads.
Numrich Arms, Internet or Make Them.
Try http://www.canadiangunnutz.com/
The value is $40-$150 depending on condition, location, need etc.
A bolt action shotgun in 12 gauge.
50-100
http://www.histandard.info/manuals/sears/bashotguns/index.html
The value of a 16 gauge bolt action Kessler shotgun can vary significantly based on its condition, age, and specific model. Generally, prices can range from several hundred to over a thousand dollars. To get an accurate appraisal, it's best to consult recent sales, check online marketplaces, or contact a firearms expert or appraiser.
Kessler. Only in business from 1951 to 1953.
Sadly absolutely perfect condition, the value is only about $300 USD ranges in price between $35 - $300 depending on the shape of the gun.
You can download an owner's manual for free at Remington's web site.
You can get a clip or magazine for a 20 gauge model 228 Kessler shotgun from one of several gun parts catalogs. These include Cheaper Than Dirt and the Numrich catalog.