There are a couple of methods, First and easiest is a 1 piece base made for the TC Hawken. and screws to the existing rear sight holes Available from many of the large retailers like Midway USA Cabella's and Thompson Center. With the base you can choose your rings or even use a scope you may already have, and be able to remove it for cleaning the gun. The second is having the barrel taped for rings, several style are made for this application also, and from the same retailers.
750
100-300 USD
50- 250 usd
You will have to call TC for the information. No published data.
100-450 USD or so depending on specifics
Want ad, gun shop, gun show, egunparts
100-400 USD
Contact Thompson Center Customer Service through their website. T/C generally uses name instead of numbers.
"Best" is a subjective term that depends, among other things, on your skills, intended use, pocketbook, "feel" of the weapon, etc..
They sell between $125 and 250 depending on condition caliber and extras (scopes, stocks, 209 primer conversion)
Trywww.gunbroker.com or midwayusa.com to get an idea what they are going for, and see how your local gun shop compares, depending on features they range from 300 up in retail stores. I bought mine at the factory after taking the tour of Thompson/Center and watching it be built. Great in-line, have had it 2 seasons now and it has been a flawless performer.
With the exception of guns like the Thompson/Center, a single shot weapon that changes barrels, there are few .22 pistols that can EASILY converted to a larger caliber. The .22 is a rimfire, and firing pin is in the wrong place for a centerfire cartridge.