Uighurs can certainly be found not only in Xinjiang, but all over China and neighbouring countries. Some of them are street vendors or have restaurants. Having studied "the Uighur look" now, I think the indescribably handsome shashlyk-maker I ogled at a grill in Ulaan Bator could very well have been Uighur. (He was dressed in all black and standing at the steaming grill outside in the blistering summer heat, acting all cool and friendly and efficient. Of course, I was once again much too nervous and embarrassed to interview him or ask him to let me take his picture ...)
In Chinese cities, it seems there are quite many Uighur street vendors who sell a kind of traditional sweet cake with nuts and fruit. I found some pictures of it on Flickr:
In Shanghai - by MFinChina. She writes: "A bunch of guys from Xinjiang and their nutloaf. Another person commended me for being brave enough to take their picture -- these guys have a reputation for being tough and harassing lone women (which I have experienced myself), although the Uighur guys who sell meat-on-a-stick near my house are all nice."
In Tianjin - by Matthew J. Stinson.
Samer! has another picture of an Uighur and his loaf, this time from Beijing.
If anyone who happens to read this knows more about these "fruit cakes" or "nut loaves", do tell! They look really tasty. I'd like to go to China just to try this ...