I was at his house a few months ago, and I picked up the blue film for Asteroids deluxe. I remember him telling me about the BZ bellows and he said he makes them up in batches. Maybe he just hasn't had enough inquiries to make up another batch.
I only have one, but if the demand was high enough I'd pull the other one out of the joystick. As long as I can get enough to buy a set of the RAM Controls remakes...