Anybody know where to get these from?
I'm putting together a lefty upper in 22 LR.

Disregard.  Noticed you are talking about rimfire.

CMMG list the left hand conversion bolts.  Initially Stag Arms were the only source for left hand 22 LR conversions.  Later other vendors including CMMG, PSA and Midway USA or Brownell’s started carrying left hand 22 conversions.   I can’t find the left hand collar on CMMG or Stag websites.  I suggest you call CMMG or Stag to see if they have the collar in stock.   PSA list the left hand 22 conversion bolt but I couldn’t find a left hand collar.

https://cmmginc.com/?s=22+LR+Left+hand+conversion&post_type=product&orderby=popularity

Black Dog Machine still list a left hand 22 conversion kit on their web site.  I believe this kit was sold as a Target Master but I believe Target Master 22 LR conversions are no longer being manufactured.   If all else fails you could take the chamber insert and mill it into a barrel collar.   Another option might to be Contact Beyer Barrels to see if he knows of a source for left hand barrel collars.

http://blackdogmachinellc.net/ar-15-22-lr-drop-in-left-handed-conversion-kit.aspx

Thanks for all the help.
CMMG can sell me a collar, just have to ask for it.
Are the barrels specific to right hand or left hand? Can I use any AR15/22 barrel in my left hand upper with the left hand collar?

I just received a 9" dedicated 22lr barrel.  It has a slot/groove/notch on the right side of the barrel where the extractor will engage to strip the round out of the chamber.
None on the left.

I am transitioning from a converted 556 upper to a dedicated 22lr barrel.
I also bought the collar that replaces the 556 chamber adapter.

I think you’ll have to relieve the end of the barrel to accept the left hand extractor claw.  If your careful it shouldn’t be difficult as long as the barrel is not mounted in the receiver.  I once opened a DPMS Gen 1 barrel to accept a CMMG collar.   The relived area on the right side of the barrel for the extractor claw should be a non issue.

Interesting, CMMG just messaged me and told me the barrel is not specific for right or left hand.

This is what I received:
"The collar and bolt are specific to left or right hand, the barrel isn't. Do you already have a left handed conversion kit, and are just looking to make it dedicated as .22?"

Anybody have a picture of the receiver end of the barrel to show me the slot?

I can’t get to my CMMG barrel right now and was going from memory but I also looked at pictures of the barrels posted on Right to Bear web site.   You might not need to modify the barrel.   I have never messed with a left hand CMMG/Stag 22 LR conversion or dedicated upper but have seen it discussed on forums numerous times.   Be sure to post pictures of your build and any specific information on your left hand build.   Dedicated left hand rimfire uppers are not all that common.

Here is a page showing a CMMG barrel and you can see the face of the end of the barrel.  At three o clock you can see where the opening is relieved a little for the extractor.

https://www.righttobear.com/RTB-22LR-Barrel-M4-4140CM-SBN-22LR-p/rtb22lr45m.htm

Here's a photo of one of my CMMG .22LR, AR-15 barrels.  The other one looks the same. A clearance notch is indeed cut into the barrel at the alignment point with the collar's extractor cut.  So, the barrel is "handed" right or left. [The photo was originally taken to show the slight bevel (radius, relief, chamfer, etc.) at the bottom of the chamber lip that was done to aid feeding and overall reliability.]



There is an alternative solution that I've not done on AR-15 .22LR barrels, but have done on another .22LR barrel.  Remove or grind off the alignment lug that is at the top of the barrel where the barrel interfaces into the slot in the upper receiver (the lug can be clearly seen in the photo).  Drill and tap the barrel for a set screw 180 degrees from the original lug location and install a set screw to act as the alignment lug.

MHO, YMMV, best of luck, and be well.

ETA: If you do flip the barrel handedness as described here, you'll probably want to use a bottom tap.

Thanks for the clarification and pictures SecondAmend.

You're welcome.

Thanks for the info.
That's so weird that CMMG told me the barrels aren't "handed".
I'll try calling them again.