Can you get a document that certifies the lack of birth certificate? If the birth certificate is not available, then you can provide a certificate stating something to this effect. This is common for places where birth records are not available. Affidavits from relatives may help as well.
Yeah, this is a bad situation. Since the Khmer Rouge wiped out the records, there's not a lot of choices for you. My VN wife says if you don't get anything from the Cambodian consulate, perhaps try going to your province in Vietnam. It may take some coffee money (bribes), but it can be done. The Americans know of this issue - it's not uncommon. Try to find as many family records (on your mom's side) that you can, especially if they are Vietnamese records. Get as much as you can and then ask the American consulate in Saigon about the matter. My wife's BC was pretty bad, but it was accepted. This is life in SE Asia - the Americans know it. Keep trying - you'll get there.
