@Vincent NL, yes definitely a small side street on the north side of the bridge on the east side of first ring road. If you go there to the corner of first ring road and ShunJiang Lu (顺江路) by the pedestrian overpass someone is certain to ask you if you want to buy a bike (买车、mai che). They will take you down a little alley away from first ring road and there are a ton of small “shops” i.e. rooms with bikes for sale. Shop around (more than one room) and bargain hard.