Mike:
When I attended the LCCA Convention in Dearborn in 1993 I remember going to many train shops while we were in the area. I’m sure many of those shops are no longer in business.
Have you tried this site which may or may not be up-to-date? Model Train Hobby Shops and Hobbystores Locations Directory - Find the Closest Model Train Hobby Shops and Hobbystores Locatio
If you can avoid clicking on all of the ads it shows 2 shops in Plymouth which is not far from Ann Arbor. I remember going to one in Plymouth when visiting my brother-in-law in nearby Canton Township.
HTH,
Bill