You will need a gunsmith to drill and tap the reciever to install a scope mount. Early 22 rifles did not have the dovetail grooves.
It is possible
Contact Ruger
$25-$50, depending on condition.
50's or so
No, the scope is for airguns and .22 rimfire...not airsoft Yes, You can get a 12mm to 20mm adapter.
One can be made
You have a Grade I Browning takedown semiauto .22 rifle made in Japan in 1986. Browning offers a scope mount for that rifle, their item #12333. Aftermarket mounts are available from Leupold, Burris, etc.
Well, it depends on what you have. The 10/22 comes with a proprietary rail, and is tapped already for a scope. If you have one which isn't, you need to decide what sort of mount you want. You might want to add a Weaver or Picatinny rail, or you might want to mount the scope bases directly into the receiver. Once you've made up your mind, then you get it tapped for a scope.. I'd recommend you leave this to a qualified gunsmith.
Go here: <http://www.havlinsales.com/> Click on .22 parts & scroll down 1/4 of the page for MOSSBERG .22 SCOPE MOUNT For models 26B, 26C, 42A, 42B, 42C, 42M, 43, 44US, 46A, 46B and 46M.
Best left to a good gunsmith
You need to talk to a gunsmith.