Sure you could buy a pre-made spray paint can safe but what's the fun in that? I mean, it doesn't appear to be that difficult to craft one of your own out of an empty can.
Besides the used can, you just need a can opener*, PVC coupling, two-part epoxy, sticky-back craft foam, masking tape, and a rotary tool with sandpaper attachments. This tutorial by Instructables user seamster shows you how.
*I'm wondering if one of these Tupperware can openers would work better to take off the bottom of the can. It pops the seal off of (regular food) cans instead of cutting into them which means there are no jagged edges.