I am also a huge fan of the mach 2 round, you can get the ammo from ammunitiontogo.com for 4 bucks a box. even in stores, remmy/eley, cci, horny, goes for about 6 bucks a box.
plus with the mach 2, your rifle may be able to shoot the 17 aguila round. It will definitely shoot it, but it may or may not be as accurate as your regular mach 2 rounds. I know, because I shoot 17 aggies all the time. My rifle happens to like them quite well. You could also get a remmy 552 speedmaster, or fieldmaster, or pump master. they shoot 22 short, long, and long rifles. I have a speedmaster, which is semiauto, and love that thing. Plus it is the only rifle so far that I have found, that can shoot the massive Aguila sniper sss 60 grain rounds, both accurately , and without keyholing them almost instantly.
Also a marlin 80 or 81 series, has been made for about 70 years now, new they are called 981's, and they are bolt action. They can shoot short, long , or long rifle as well.
One more thing, if you have not allready, take the front barrel(bbl) band off of the front of your rifle. See if that doesn' thelp accuracy a bunch.
Then try tightening up your v-block, under the bbl., making sure that your bbl is not loose, so to speak. Try those two tings first, if still not accurate enough for you, try going over to rimfirecentral, and go to the classifieds, and see if you can buy a better bbl. If you do all of this, and still not accurate enough for you, then get one of the above rifles I mentioned.
