Quick update on my quest for biker jeans: I found one in the Russian market behind the Kuntai Hotel on Chaoyangmenwai Street. They are not completely lined with kevlar, but have huge patches all over the back, the shins and knees. It is a "Lindstrands". Doesn't look like a fake, more likely they left the factory through the backdoor.
Looks too long when I am walking around, but just right when I am sitting on the bike.