It may not have one. Contact Browning.
Try gun shops, on line auctions, egunparts, pawn shops and gun shows.
Get the serial number off the gun. Go to Browning's site, click on Support then date your firearm.
Browning Arms Co. did not make or import any pump action shotguns in the 1950's. This gun was made by another manufacturer and could possibly say "Brownings Patent" on the gun. John Browning invented dozens of guns that other companies made. This may be what is throwing you off. Check the gun again and find the manufacturers name. It is likely a store brand such as Sears or Western Field.
The Deagle is a gun in of itself. It isn't really based on anything, unless you feel that because it is a locked-breech gas operated gun that the design is copied from John Browning.
It would help if you stated the model.
website is called Numrich I just got one off of there for the exact same gun. Find your gauge and model and it will be there its 40 but worth it.
Try Numrich Arms, also known as Gun Parts Corp (GPC), they have a website but you're better off calling them.
There was the Browning M1895 "Potato Digger" (which was much different from the Vickers), and the Maxim machine gun (on which the Vickers was based) went into production shortly before the war kicked off.
Take it to a gunsmith
Try gun shops, gun shows, on line auctions.
call browning but dont mess up that classic gun with a scope. you would be better off selling that gun and purchasing a deer set up and putting money back in your pocket.
The Browning 22 auto was traditionally scoped with an integral scope mount base that was mounted to the barrel. The mount rides up above the receiver and rearward toward the ejection port. Grade I is supposed to also have the groove mounts. The groove mount is not recommended because if the gun is taken down, the scope would be off zero when the gun was reassembled. Browning offers the integral barrel mount base and rings for this application. The Browning part number is 8517, however, your older Belgian model may not be tapped for the screws and may require a gunsmith to tap and thread the barrel. This was confirmed in the 1964 Browning catalog. Recommend you discuss this with the Browning Customer service dept at the link below to verify. No other cross references could be found for mounts that fit the Browning 22 automatic rifle.