I bought some for curiosity at Green Diamond (tractor dealer), maybe a year ago. If your nearest one don't have it, they'll probably bring it from another store if it's around.
There's guys who show up at the huntin' & fishin' trade shows that want you to swap your evil lead ammunition for non-tox. Weren't they working this through DNR? I'm sure there's a blurb in the Hunting Regulations pamphlet. If so you should be able to call up an office and exchange box for box. (Your tax dollars, hard at work.)