My last ammo cans from Cheaper Than Dirt... without a doubt the worst cans you could imagine... heavily rusted, dented, no lid seals, one so badly bent at the hinge they'd removed the lid so they could pack it in the box... 2 of the cans that did close were 1/4 filled with some skanky water that had leaked all over the box... never again.
I've gotten 16 50cal ammo cans from Sportsman's Guide and these things didn't even look used. I figured the first 4 I ordered were a fluke so I ordered 4 more and they were even nicer... They were $12.95 for 4 cans, SG hits you for a $5 extra shipping charge per 4 cans but you can counter that with a coupon...
SG is out of stock right now but watch their website... The other option is a funshow or surplus store were you can see what you're buying...