Good question

It must be possible as cars and trucks cross the boarders everyday

from other country's

but getting them registered in China  might be the problem

Before I came to China (nearly 3 years ago) I was looking into importing my car, I was told 100% import duty on all imported cars. I didn't look any further than that though.

I would contact some of the classic car clubs in China. They must know someone who has brought in oldies from around the world (can't all be party member cars from yesteryear) 

e.g. http://www.classiccarchina.org

Remember if it is imported and unique in China, keeping it running might be difficult. If you just want to bring you old VW Golf from home, then it is probably possible, but must be easier just buying one here. 

I did have this thought as well a couple of years ago when we considered a car, e.g. something from the VW dealerships here just isn't the same as in Europe, less horsepower, less fuel efficiency (and of course these two are down to the shitty quality of the gasoline) poorer build quality, less choice of options, and less airbags and security stuff

Once upon a time, it used to be feasible for a foreigner to import a car into China.  The rule was one new or late-model car per foreigner, duty free.  But alas, too many CCC's (Clever Chinese Cheaters) exploited this loop hole to run a profit.  Mainly Chinese bosses with foreign workers, having them bring over cars that were then sold without the usually high taxes associated with imported vehicles.  Now, if you want to import a car, it has to be done through a registered vehicle importer or dealer, and you will need to pay the normal import duties to have the vehicle clear Chinese customs.  AKA, not worth it.