Yes, what Motokai & Euphonius suggest is probably the ticket.

I have heard this from several official sources, and also have a little personal experience with it - organize some unique tour that is a win-win situation, and doors will slowly start opening. Especially if there is positive media coverage.

A classic bike tour might be the way in. Include some Chinese classics, maybe a BMW classic, perhaps a Ducati classic (i.e., bikes with a presence in China), and it can probably be put together. I'm chasing a very specific classic XingFu 250 and, if I can convince the stubborn/crotchety owner to sell, I'd be thrilled to join you.

Under these circumstances, all the "special permissions" can fall into place through the central Beijing authorities. In China, Beijing is considered the center of the universe, so the various provinces wouldn't give anyone any hassles, if you have the infamous Beijing "red chop". One strange requirement (as I have just learned from one project) is that you'd probably have to fly a "friendship flag" from the bike.

The Harley distributor for China might be a good initial point of contact. Or, if you are a member of H.O.G., it can certainly help you out (HOG China). I just read an article in HOG Tales about a couple of Harley Ultras riding to Tibet (Everest Base Camp). They like that stuff here.

But, doing it independently, as ChinaV notes, is going to be extremely difficult (I'd guess practically impossible) ... or illegal.