I have not personally sourced from any of these suppliers, but a quick google search reveals a lot of information out there. Start calling and price checking on bulk NGS. Depending on your needed volume and desired final product, there may be a lot of variability.
Cheers!
MGP (Achison, KS):
http://www.mgpingredients.com/product-list/Grain-Neutral-Spirits.html
GPC (Muscatine, IA / Washington, IN):
http://www.grainprocessing.com/corporate-info/facilities-services.html
Alchemical (Ashland, OR:
http://organicalcohol.com/store/index.php/products/
Archer Daniels Midland (ADM - Peoria, IL):
http://www.adm.com/en-US/products/food/alcohol/Pages/default.aspx
CVEC (Benson, MN):
http://www.cvec.com/190-proof