Hope this helps!
http://hochiminh.usconsulate.gov/faq3.html
How can I obtain for my birth certificate? In case, I cannot obtain my birth certificate, what can I do?
Individuals born in Vietnam who need new copies of their Vietnamese birth certificates need to contact the office of the People's Committee of the district where they were born: the district where their mother was then resident according to her Ho Khau. The district People's Committee can issue certified copies of a birth certificate (Ban Sao) based on their records of the original birth certificate. Alternatively, the office may provide an Extract (Trich Luc) of the information in the birth record on file in their office.
If you are not able to obtain a birth certificate because records have been destroyed or the government will not issue one, you must obtain a statement to that effect from the civil registrar’s office and submit secondary evidence of birth. Secondary evidence of birth can be old family household registrations, school records, or baptismal certificates.
How can I apply the Police Certificate (Ly lich Tu Phap)? Can your office assist me in this matter?
If you live in Ho Chi Minh City, you may contact the Justice Department at 143 Pasteur St, Dist 1, Ho Chi Minh City, Vietnam. The telephone is 848-829 7052/ 848-822 3276. It is our understanding that a friend or relative may request the Police Certificate (Ly Lich Tu Phap) on your behalf. This can also be done at the local Department of Justice office of your last residence in Vietnam.