It turns out there are, in fact, some user-made maps for Mirror's Edge, to my surprise. There don't seem to be very many, but they're located on the fan site On Mirror's Edge.
There's also some DLC available for it -- the Pure Time Trial Map Pack, which, true to its name, is a set of maps without combat. However, the environment is not the city rooftops from the original game, but sets of abstract shapes floating in space. If you ask me, I think taking away the urban environment pretty much strips most of the "parkour" out of it.Those who want it anyway, who own the game on Steam, would normally be out of luck for some reason, as it doesn't officially work on Steam. However, the same forum listed above has a workaround available to allow Steam users to play the maps too.