West, North West there are a few shops in the Livonia/Farmington area, but I haven't been to them. Nankin(?) hardware in Westland(?) might have something, though I heard they downsized the trains.
Tony's Mower shop, and a little shop in Plymouth are nice little shops, but I doubt they have On30.
If you do end up south of Detroit, Keck hardware "do it center" may carry some Bachmann On30 but it is a rather small train section.(west road, a few blocks west of Fort st. in Trenton).