You can find them at the Wisconsin Cheese Mart on State Street in Madison, the UW Bookstore at Hilldale Mall, and various gift shops in the West Towne Mall area.
The official Original Cheesehead Hat is available directly from the team. buy a cheesehead
Authentic cheeseheads are manufactured using a specialized polyurethane foam production process. Cultural Significance Philadelphia cream cheeseheads has a nice ring to it You can find them at the Wisconsin Cheese
Platforms like eBay often list vintage or "original Foamation" versions from the late 90s. Manufacturing & Trademark the UW Bookstore at Hilldale Mall