I did manage to disassemble the dash, and here's what I learned. As far as I can tell, the screws really are T33, and T33 drivers are more or less impossible to find in North America (even at Wiha Tools, which otherwise looks great--thanks for the tip, MINICHEF). However, since little torque is required on these screws, a T30 driver will do the job. Thanks for the help!

 

If you're looking for security bits, try Harbor Freight. This set is even on sale right now.