Delafield: Candy Concepts (website) (new fixtures no gondola)
Roberts: Phoenix Fixtures (website) (New Millwork)
Balsam Lake: Bishop Fixture and Millwork (website) (New Millwork)
There is NOT a gondola shelving dealer in Wisconsin, but here can find the best alternative.
First, start with local classifieds like craigslist (website). Look for liquidation sales in Green Bay, Milwaukee and Madison. Check out of state, too, in cties like Chicago and Minneapolis.
You will find serious used store fixture dealers in Michigan and Minnesota, and in Illinois dealers for NEW gondola retail shelving.