There are a couple of version of Mach available for the PA.
The one we originally did at Utah, and the more recent work done
by the Open Group (The Organization Formerly Known As OSF) which
was based on the Utah work.

Both are available under BSD-style copyrights, both contain code
freed up by HP.  Neither supports PA 1.0 boxes (e.g., the 835).
The base architectural changes needed to support 1.0 are minor
(we originally ported Mach to an 835) but device driver support for
the CIO bus is severely lacking (we had drivers for LAN, HPIB disk,
serial ports).

A NetBSD port is presumably primarily going to be targeted at the
PA 1.1 boxes (705,710,712,715,720,725,730,735,750,755,J200,J210).

As far as I know, no one has ever done PA 2.0 (e.g., J280) support.