You don't say where you are located, so I cannot give you a definitive local place to try but you should have gunsmiths nearby. A good place online to get them would be advancedrifleparts.com
Depending on the gun, yes.
gun shops, gun shows, want ads
Try gun shops, gun shows, on line auctions.
weaver refers to the type of scope mounts the scope uses. a weaver scope can mount on any rail size.
Check with any good gun shop or sporting goods store.
Scope mounts are available for purchase online and in many stores. They can range in price from $20-$150 or more. Your local gun store, Cabella's, Gander Mountain, or Bass Pro Shop would all have helpful staff that would be able to assist in choosing the best option for you.
Are you trying to fit on a gun or rifle ( you said gun) What model are you asking about,. Is it a scope designed for pellet rifles. How big its the dovetail on the rifle. You need to be more specific.
Gun shows, gun shop
a mount that fits on rail fitted to a gun that alows a sight to be seen higher above the gun, making it easier to aim.
The auction website eBay is a great place to start your search for scope mounts for a 1951 Savage 99. You can also try visiting pawn stores or gun shops in your area.
One can purchase rifle scope mounts from websites like Optics Planet, Cabelas, Amazon, Scope Mounts, Airgun Depot, eBay, Talley Manufacturing and Jmecks Scope Mounts.
Only if the airgun has a scope rail designed into the gun. You will also need an airgun scope not a firearms scope.