I wish I could be more specific, but I want to think because of the "new interest in rimfires" supposedly brought about by the HMR, that someone was being courted to start producing 5mm rimfire ammo again. I know this doesn't help any, but maybe give you some encouragement to keep looking around. Maybe it's out there by now. Otherwise, you'll probably have to keep an eye on gunbroker. If you have any local gun shops, ask if they know of any sources.
The bayonet cannot be abolished for the reason, if for no other, that it is the sole and exclusive embodiment of that willpower which, alone, both in war and everyday life, attains its object.—General M. I. Dragomirov