Need more information. Value will depend upon original maker (F.I.E. was the importer) and condition of the firearm.
100-500 USD or so
The Sears Model 42DL .22 caliber rifle was manufactured by Marlin Firearms, their Model 80. Check with Marlin for parts availability.
100-500
Can't be determined from the markings you list.
Try gun shops, gun shows, want ads
Firearms International was an importer, now out of business I believe. It is unlikely that they would have actually marked the gun with their name before these markings were required in 1968. There are probably other markings that may identify the actual manufacturer. Double Action refers to a revolver mechanism and I have no idea what you mean by a doubleaction trigger on a rifle.
Short action.
Do a web search on "firearms suppressors"
100-400
It depends on the particular model of the rifle, not the caliber it is in. What model and make is it?
100-500
Old gun catalogs from the 1960s