Found a source for ammo cans, and while they aren't dirt cheap like that one guy who used to be a MWCA shows (you could get 5 40mm ammo cans for $6 each, and if you just wanted one, he'd gouge you for an extra buck and charge you $7), they do have the larger sizes and all of those are being sold for $20. If you figure it out on $ per cubic inch of space, 20 bucks is a bearable price. They have 40mm cans, somewhat larger 20mm cans, and the almost suitcase sized 25 mm cans. Some have the sides bowed in, so shop selectively. Sadly, the "fat 50" cans are also $20, as well as normal 50 cans, and the 30 cal cans are $12, and that's no bargain. For loaded ammo, a 30 cal can is perfect, and there's no way you could lift a 40mm can full of loaded 45 ammo. But for storing guns, or empty cases, or powder, or primers, these bigger sizes are good.
The source is CC Surplus on White Bear Ave. North of Hwy 36 but South of Maplewood Mall, and they have GREATLY enlarged their square footage and inventory since the last time I was in there several years ago. Well worth the trip if you haven't been there in a while. Prepare to wander around getting tacticool lust for the better part of an hour drooling over stuff that you'd like to get if you didn't have to keep making house or rent payments...