Hey,
The first place I’d check is Chunxi Lu. Although there are a lot of high priced shops there, what you should look for are the touts who hang out in the plaza. They’ll approach you asking if you want shoes, clothes, etc and generally they’ll lead you to a network of apartments that sell fake goods. Some of the stuff you can find there is good quality, and almost all of it is very cheap. I’d be willing to bet you can find what you’re looking for there.
The other places that you checked (Renmin Nanlu, 1st ring road intersection, Wuhouci) will have jackets like the one you describe but they’ll be high priced. Good luck!