Why do These Cylinder heads Never show up for Sale??

If they’re like most other MP heads...... the initial cost was probably way high, and they needed a bunch of work done on them before they offered any real benefits(or could even be used).
Couple that with the fact that there have been many horror stories of MP heads with difficult to correct manufacturing defects(think w5 and stage 6)....... and it’s probably not too hard to figure out why they weren’t that popular.