Star Wars addons!!!
*descends into a gibbering, drooling mess just thinking about them*
AFAIK the only MTT and AAT addons made/planned are part of the very much anticipated and looooooooooong awaited for
Galaxy at War mod.
I check the GaW site regularly but it does appear Acaycn has lost motivation for the project and has other RL commitments that have got in the way
Unless the mod ever sees the light of day I'm afraid you are out of luck and there aren't really enough addons to make a decent Star Wars mission with IMO until then.
edit:
There are some Trade Federation droids available here
CaptMoore mod