you can find a used pro-m in the classifieds fairly easily. i also believe that the former employees of the company have reformed under a new name. do a search and im sure you will come across it.
With the older ProM company and their mafs the 77 & 80 had the most accurate electronics but like most things, they made you dig a bit deeper in your pocket for that quality.
Can't say that info is still valid but you could always call them up and talk to them a bit.
I have seen on more than one occasion Don 95Vert say the last run of mafs from the old ProM company had some issues with accuracy.