BudsGunShop.com - NAA PUG 22 MAG CONVERT TO / 22 LR CYLINDER ??

Copied from the manufacturer's web site:
Can I order additional cylinders?
Absolutely. LR-frame guns can have additional LR cylinders; Magnum-frame guns (including the Black Widow and Mini-Master) can accommodate either LR or WMR cylinders, regardless of their original configuration (some people originally order BWs and MMs in LR only). However, we require that the gun be returned to us so that we can assure ourselves, as well as you, that the gun is properly timed. The necessary (and absolute) alignment of the chambers with the gun’s bore is critical and often requires a little tweaking of the cylinder star &/or hand &/or bolt.
For technical information, you can call them at: Toll Free 1-800-821-5783
Or email them at: info@northamericanarms.com
Hope this helps.

Some of them can be converted, but require you to send them in for cylinder fitting.