Buying second-hand winter clothes in northern China

Yesterday I crossed the point in China where the weather changed from "cool enough to put a jumper on a night sometimes" to "You need more layers". And I am continuing further north to Ulan Bator, Outer Mongolia.

As I began the trip in August in Southeast Asia I did not bring warm clothes because they can be bulky and I expected them to be easily obtainable, even cheaper, once I needed them when in a cold location.

I'm now in Xi'an in Saanchi province. It's a big city and I'm staying in a backpacker hostel here. I asked at the desk if there was somewhere I could buy used/second-hand winter clothing. They looked quite puzzled as if nobody would ever think of such a thing in China.

I've bought used clothing easily enough in other developing countries with cold winters. Such shops were everywhere in Georgia. I also know it's easy enough to buy used clothing in developed western countries like Australia and the US. I've even bought used western clothes in a big trendy store in Tokyo where there seems to be a certain niche for such things.

Even though there's more and more rich people in China and luxury malls are everywhere, most people are still poor. Is it really the case that the non-rich in China don't buy and sell second-hand clothes? How can I find such places? Is there such a shop in Xi'an?

I'm expecting cold but dry and not windy. I expect to need a coat, gloves, and warm socks. A traveller heading south already donated a pair of longjohns and a cashmere shirt/jumper. I have a lot of extra cotton layers.

(I know I can buy inexpensive new clothing but as a non-winter-specialist I'd have more faith that a used but known brand would perform well, than a new but obscure Chinese brand.)