Wilburn Parks,
Are you looking for a supply yard to fit into your route, or are you looking for someone to deliver?
Orion Stone Depot, Orion TWP. Deliver/pickup 248 391 2490
Bed Rock Salt, Ortonville and Waterford 248 627 3240
Bushel Center of Hollow trucking 734 482 7263
or you can try the salt co's
IMC salt
Morton
Cargill
Those are just off the top of my head..I know there are more. Are you a member of the MDLA, there are always ads in there monthly publication "landsculptor"
http://www.landscape.org
Hope this helps some,
Andy