In my hands, there is no springer that is adequate out past 40 yards. If it's powerful enough to do the job, I can't shoot it well enough, and if I can shoot it that far, it's not powerful enough. That's why I switched to PCP's ;-). Sounds to me like your assessment of the 220 is also a realistic assessment of your own abilities, so kudos to you.
If you want to stay with a springer, I'd say your best plan is working on your stalking skills, try to get close enough that you feel confident in your ability to make the shot. If you're ready to make the jump to the Dark Side, a good .177 PCP can easily do what you want. The combination of higher velocity with heavier pellets, and zero recoil, makes 50 yard shots very doable. A lot of the .177 PCP's are in the 20+ fpe range, and pin point accurate out to 50 yards or more. AND you can get a repeater, so fast second shots are now a reality. Going up to .22 stretches your realistic range on squirrels to 70 yards, maybe more depending on the rifle and your skills. Of course, they also are more expensive to shoot. There are a fair number of decent guns at around $500 available now, the Marauder is the one getting all the press right now, but there are a fair number of other choices. And if you go used, you can find even more choices. Down side, you've got to fill them, and that can add up quickly. For more info on that, check out this post:
http://www.gatewaytoairguns.com/airguns/forums/thread-view.asp?tid=19477&mid=156556#M156556 Lots of good info, if I do say so myself :-). Hope that helps, and good luck. Later.
Dave
PS Just realized this is the Classifieds, so I PM'd you on a rifle :-).