If you went to Takahashi's panel on Saturday
afternoon, you should have seen her in person.
Her autograph sessions was on Saturday and Sunday
mornings.  

Katsura was there in two of the hobby booths on
both Friday and Saturday.  

Plus Nightow (Trigun creator) and Asamiya (Silent
Mobius creator) each has at least a couple signing
sessions too.

Next time, just go to the Anime Link booth, those
guys know who and where the Japanese guests will
be signing.