You might try Patio bike shop out on Forest Home ave. They have some used parts, mostly higher end stuff, but I've bought odds and ends there. I know they tend to be open odd hours. You also might try Cory's on Murray Ave. Unfortunately Milw doesn't have a good fix up old 70's, 80's bike shop. I tend to buy stuff on line or get it from stripping bikes. The other place you might try is the bicycle collective on 29th & Clybourn near Marquette