There are some industrial RFID technologies that could be adapted, but I have yet to see a system that will work for you out of the box.
I've been toying with this problem for sports photography, but using battery powered active emitters for more reliable detection, by having a receiver that mounts to the camera, and then syncing the data in a post process. Biggest problem I have been facing is that the signal simulations I've run all did very poorly in an average indoor venue due to signal multi-path producing multiple hits for a given transmitter. It would require extra work in the receiver unit to filter out the 'ghosts' from signals the bounce off the ceiling or support columns and appear to come from a different angle.
But the active transmitters don't need to be much larger than a AA battery, and could even be made exceptionally small.
My biggest stumbling blocks on the project have been time to devote to designing and developing a suitable set of prototypes, and the money to do build the things.
Canon EOS 7D | EF 28 f/1.8 | EF 85 f/1.8 | EF 70-200 f/4L | EF-S 17-55 | Sigma 150-500