You can do team preview if you battle through the union room. Is the problem because there are too many players in the union room?
Most of the local tournaments that we run do use the union room.
But last year I had 64 players for the convention. I had to turn people away because we were under a tight time schedule. This year we increased the cap to 128 (doubt we will hit that many though)
But yeah, as you can see - the convention is way to large to have it run in the union room.