I've noticed on 2nd viewing that Wheelie knew several location of other 'Ancient' Cybertronians, before they headed of to DC and awoke Jetfire.
There were about another 6 or 7 other 'Ancients' hiding in the US alone, not even counting other Countries around the World !!!
I think these could be how more characters would be found for TF3, fitting the solutions as we're pointing out, for example these 'Ancients' could easily be Dinobots?