why not just buy the altoids tins commercially. You wouldn't have to worry about them being available and you wouldn't have to buy them in bulk. You could buy them as needed. Even if you dump the mints the cost per tin is $1.50-$2.00. I don't know what you had in mind as far as price for the containers but to me this seems fairly resonable. You could even try sharing the mints with your horse. Just a thought