Well, I believe Alpha Trion's considered one of the 13, and so is Nova Prime, so their's two more to use. I Don't entirely know all their names either though, nor do I know a damn thing about them aside the fact that I want to know more about them!
I Guess you could use Sentinel Prime, and Zeta Prime. Who else...
as for names I've created
Alpha Prime, wich was a totally different character than alpha trion, was an energy filled conduit-type Prime, resembling that of a roman god. I drew him ages ago, but cant find him...
Miriad Prime, A Master of trickery and deception, but an autobot through and through,
Luna Prime, A Master of the dark arts of Cybertron.
Psychus Prime, Later Dissolves into a mental state, hides away for millions of years, and re-awakens and succombs to a terrible accident, re-emerging as Toxitron.
Hope this helps out.
If you use Alpha Prime, or any of my story ideas or made up names, just drop me a credit line, but I look forward to reading it regardless of what you do with any of it, if you do anything with it at all. not a whole lot of people read these. I'm one of the minority.