Another Forum
Oh, man, this topic has been done to death several times on
www.rimfirecentral.com - they're always going over debates on which 22 ammo is quieter, cheaper, more accurate, you name it, they do the rimfire stuff.
A short answer, though, is that many manufacturers make subsonic 22 LR ammo, from the fairly inaccurate (such as Remington is reported to be) to the match stuff like Lapua and Eley. CCI makes "CB Longs" which are long enough to at least hand cycle in many autos, but it really depends on what you're trying to do - if I wanted to kill small game or pests fairly quietly, I'd go with subsonic 22 LR hollow points, 38 grains, and live with the extra noise. I'd shoot maybe squirrels with a 29 grain bullet.
Then again, if I wanted it to be as nearly silent as possible, I'd go with the Aguila super colibri.
If "silent" is really your thing, and you can't legally own a suppressor, just remember too a couple things:
If you fire only one shot, most people or varmints won't be able to locate you, because they won't focus on the sound until they've heard the first shot. Make the first shot count.
If you fire prone (on the ground) part of the sound will bounce
up, making it harder to locate you.