Birth Certificate for I-485

請熱心人士幫忙!! 我隨我老公申綠卡, outstanding ability 那種. 移民局通知要additional evidence.原文如下:
"Birth Certificate: Submit a copy of your civilly registered birth
certificate that reflects a timely registration and indicates both parents'
full names. Provide the foreign language document, along with an English
translation."
因我以提供出生公證, 所以實在不知要提供what, where to find. I told the lawyer we didn't have birth certificate in China in 1970s, and the lawyer called 移民局 and asked them. 移民局said "then prove there was no such thing in China at that time". I'm so much confused now. Does anyone have similar situation? Where I should go for the proof in China? Very Urgent!! Please help