Try e-gunparts.com, gun show, gun shop, want ad.
Mossberg 500.
I have one for sale. Message me @ garym6@cox.net
In front of the butt stock .
Whatever model the maker called it that made it for Sears. Go to Proofhouse.com for a store brand chart.
I have one for sell in very good condition.
The butt plate screws (2) at the end of the stock must first be removed. You will need a long shank flat tip screwdriver to remove the screw at the bottom of the center hole in the stock butt. Reverse to reassemble.
On line auctions, gun shops, gun shows, pawn shops.
LONG out of production, the company is no more. You may find a used stock at gunpartscorp, but you would need a match to the correct model- there were dozens.
Before a price can be determined we must establish what model of Winchester shotgun that you have,and determine the overall condition of your shotgun.How much blueing is remaining,how much original finish is left on the wooden forearm,and butt stock?Is the bore inside the barrel in good condition?All these factors determine the value of your shotgun.also include the model number,along with the serial number to help identify what shotgun that you have from Winchester.
The butt of a rifle or shotgun- the part that goes against your shoulder.
Best left to a gunsmith
I have a used "riot" 520-30 butt stock.