Replacement for Tektro Disc Brake for 29" muni- what's the best option?

Try just using the ‘site:unicyclist.com’ tag with Google. Works better.

Anyway this is the mothership disc brake review thread:

The most active posters there seemed to settle on the TRP Spyre/Spyke cable-operated hydraulics. Shimano Deore also got good marks in early replies.