Need more information. Value will depend upon original maker (F.I.E. was the importer) and condition of the firearm.
The Sears Model 42DL .22 caliber rifle was manufactured by Marlin Firearms, their Model 80. Check with Marlin for parts availability.
100-500 USD or so
100-500
The Sears Model 43 103 2850 .22 caliber bolt action rifle was manufactured by the well-known firearms company, Savage Arms. Sears marketed this rifle under its own brand, but the design and production were carried out by Savage. This model is part of a series of firearms sold through Sears during the mid-20th century.
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"
It depends on the particular model of the rifle, not the caliber it is in. What model and make is it?
100-400
100-500