There's this on the SWJ library:

Military Assistance and Training Advisory Course (MATA) Handbook for Vietnam - US Army Special Warfare School Handbook, January 1966.

Reference material for the military advisor in Vietnam. Reflects doctrine as taught at the Special Warfare School in the 1960's and early '70's. The handbook was prepared for use in the MATA courses of instruction and served as a ready reference for advisors in Vietnam.

There's also the more current FOUO MNF-I COIN handbook, published in May 06. It's not really an "Advisor Handbook", but it does have sections specifically targeted to those in advisory positions. If you don't have it, PM me with a .mil address and I'll get it to you.