They're in Niles, MI: http://www.fernwoodbotanical.org/

They have lots of info and brochures on native plants to the Michiana area and demonstration gardens. Also my quick google search didn't turn up a South Bend garden club, but there is one in Buchanan and one in Niles. Contact both through the Chamber of Commerce in their respective cities.

Also, does Menard's have a gardening center? They usually have good prices on other things.

Off the top of my head, I've noticed that hydrangeas and roses seem to do extremely well in your area. Also raspberry canes.