Nothing new to add, but just to reinforce what's been said, there are a lot of ammo companies out there besides the big 3 in the US (Remington, Federal, Winchester). Somebody will make ammo.
And also reiterating, for less than $100 you can get setup with a basic reloading kit by Lee. This will ease a lot of fears about ammo availability for just about anything. For most stuff (.303 Brit being an exception) you can even make brass for a cartridge from another type of case. Heck a little over a year ago I made several hundred rounds of 7.62x25mm by cutting down .223 Win brass and using .30 carbine bullets. They bulge just a smidge on firing, but otherwise work fine.