I’ve actually heavily studied the Tennessee body modification laws including speaking to doctors, artist themselves, the health department in my county and of course reading the written laws. There is absolutely nothing that prevents a certified piercer or tattoo artist from using an injector, scalpel is a different story though.
As always your best bet is to approach a professional but as you’ve said you have done that to no avail I recommend if you happen to know anyone who is in the medical field. Friend who’s a nurse? Family friend who’s a doctor? Maybe even asking your GP? Given the proper documentation and knowing proper sterile procedure they may be able to assist.