Right now, there is no central place where FACS coders advertise and are accessible. Also, there is considerable variability in experience among FACS coders. If you are interested in hiring someone, first make sure they are FACS certified (i.e., have passed the FACS final test).
You would also want to be sure they have had coding experience beyond testing. The final test simply tells us that someone is proficient in recognizing the AUs, but reliably coding real-life data takes practice.