Do you really mean a PPK/S in 22lr? If so, you can check with the links below, but I don't really know. I'd take it to a gunsmith, or send it to the first link below. If, on the other hand, you really meant the new P22 that looks like a P99, then these links will get you there.
He has both the 5" and 3.4" barrel kits for sale for the P22. I don't know if he has the 5" in stock, but I know he doesn't have the 3.4" until February, as I have one on backorder (and this info is from a phone conversation I had with them). Otherwise, you can try :
Poor recovery. I flashed through your post annd read P22 instead of PPK/S. Tried to edit my way out of this boo-boo, just made things worse. Sorry. Earl's is still an option, if you have a German man. gun. (He doesn't do USA man weapons. Otherwise, the second link for Walther USA should be able to steer you in the right direction.