I'd start with Eichten's Hidden Acres in Center City, MN. They supply the buffalo for many Twin Cities stores and restaurants.
Eichtens Hidden Acres
And I have a pound of buffalo in my freezer from Lofton Ridge, Chisago City. I think I bought it at Farm In The Market (Midtown Global Market) - you could give them a call to see where they get their buffalo. Or see this web site for Lofton Ridge's contact info:
For more possibilities, see the Minnesota Grown directory. Wonder of wonders, it's searchable online! (So now I don't need to lug around their printed directory at the State Fair!)
Eichten's Market & Bistro
16440 Lake Blvd, Center City, MN 55012
Farm in the Market
920 E Lake St, Minneapolis, MN