Tom,
There is a great airgunning resource at http://www. airguninfo.com
Many on-line dealers and helpfull topics! Ya might find the sorta "Local" info you need?
Diana offers several mid-power .22's in the Model 28 family. Unfortunatelly, todays "Magnumitis" trend has created rifles of high penetration that are unusable in metal sheds.
I know your dilemmia... I had to kill some Feral Pigeons in our Horse Arena once, and had to go to a 650-700fps .177 to prevent shooting holes in the tin roof. I used Head shots and backed each up by aligning with wood beams to take any misses.
I first tried a 500FPS .22 and it wasn't sufficent to pierce wing bone, then tried a .177 Match W/C @ 650-700fps but it didn't penetrate said bone either. I finally ended up using the .177 with a scoped rifle at that velocity firing a Crosman Point. It did the trick out to 40-50 yards, even when only a chest shot was available, it did not over-penetrate.
Doggone Pigeons are big birds and need to be hit well to bring down. Also, having the overpenetration concerns and using a .177 "Light Sporter", a follow-up kill shot was necessary. I don't like sloppy kills, but with these Building preservation restrictions coupled with the fears of Disease concerns for the horses feed, I saw that shooting and eliminating the Pest Birds was paramount. In truth, a higher powered/ Larger Caliber rifle would have most "humane" but just could not be applied.
Maybe in liew of purchasing a special rifle just for this, maybe a shooting buddy has one you can borrow? However, a fella always needs an excuse to get yet another air rifle tho...
Good luck & HTH,
ZVP