check with your Vietnamese friends and colleagues to see if there is a guitar club anywhere.
I was invited to a "guitar concert" last year in Hanoi. The members of the club were performing, and they had several invited guests, including a couple of European folk music performers. The last person to paly in the evening was the diector of the club - played classical guitar and literally blew everyone else away! He is an incredible player! Absolutely stunning! Why do I add this detail? Because if there is a guitar club in HCMC, there are probably some very, very good players and instructors in the club!