It can be incredibly frustrating to find slightly odd-ball calibers like that. My father has a couple of old lever action deer rifles that he's inherited, and they can be lots of fun to track down ammunition for, since some are larger caliber rimfires that are virtually extinct, and the rest are tend to be odd flat-nosed Winchester cartridges, to accommodate the tubular feeds.
What's the larger caliber rimfires? I've only read about them, and from what I've heard in passing about the dangerousness of making rimfire ammo (in relation to one of the reasons US manufacturers aren't contemplating expanding production), suggests you're out of luck there.
The classic centerfire flat-nosed Winchester cartridges, though, you can of course reload them after getting some modern ammo for it (don't try this with old mercury fulminate primed ammo, I read an article by someone who had an old Browning police semi-auto carbine, he wrecked it because the mercury fatally compromises the strength of the brass). My father has or had one of those, I think it was from the era when you could buy one with the same ammo for your handgun as your rifle, the action certainly wasn't very strong. Octagonal barrel, a really neat piece of history.
Ah, and for those who aren't into this sort of thing, all the "calibers" I mentioned in my above comment use bullets of the same width, it's a confusing "system", if you can call it that, it grew organically.
