1- You can get one from Lexel: [Finished] 5. Batch "TA" Bistro HD OTSM/Narsil drivers, 15-47.5mm size fit H03, MF01, MT03, Q8 1S or 2S, Clicky or E-switch or from led4power: Led4power.com : LD-4 CC linear drivers, ILC-0/1 illuminated tailcaps, optics, MOSX, copper DTP MCPCBs...
With that said, I dont think your light has something smaller than 15mm I might be wrong but most AAA lights use 15 to 17mm drivers.
2- Terminology - Flashlight Wiki
3- Yes and Yes.
Good luck!
P.S.
I am a noob my self 