After reading the OP's original request, I think he actually looking for a .22 conversion kit. These kits are available, but they are all collectibles... so they won't be cheap. The last one I saw for sale was between $600 to $1000 for the complete kit. These conversion kits contain all that is necessary to fire .22LR in a standard 9mm Luger. The consist of a replacement rimfire toggle assembly, an insert barrel and a magazine. No permanent modification of the standard Luger is necessary.
If you prefer a more permanent solution, all you need to find is the toggle and magazine and any competent gunsmith that can barrel a Luger can built a .22 caliber barrel to work with these parts. Still a very expensive solution, and you don't end up with anything collectible. If all you want to do is shoot .22's from a gun with the same grip angle, I would recommend you spend your money on an original Ruger .22 semi-auto... they are loads of fun, and would be much less expensive than converting a Luger to that caliber.
here is a link to an album on this site that shows the .22 caliber components.
http://forum.lugerforum.com/album.php?albumid=375