Usually, you can go to the manufacturers website and find their contact information, unless you are talking about a manufacturer that no longer is around, then you may want to find a historian in regards of firearms.
Contact the maker.
Contact the manufacture or look it up in a Bluebook of gun values.
Yes,www.proofhouse.com
A gun manufactured by Browning Arms
Contact the maker if still in business. If not, try the Blue Book of Gun Values.
From what I could find your gun is made by Winchester. It should say it on your gun somewhere though.
Such an item would be a custom piece. None are manufactured in that configuration.
You ask the question here. State the model number and who manufactured the BB gun. I need those 2 items in order to give you an answer.
A cannon
Blue Book of Gun Values or proofhouse.com.
1972
USA if you mean Ruger.