I bought mine at Big Al's a few years back so maybe they can still get them.
Sander's is imported to the States by
Quality Marine, and they show them on their website but you still need a dealer. They also import Tropic Marin stuff.
I bought my Tropic Marin salt from
Aquarium Obsessed in Ontario so maybe try them too. If you find a dealer let me know, I need to get my 50mg fixed.