Marriage certificate for a foreign couple

We are both foreigners (from the same country) living in China, have been living together for three years as spouses and have two children. we have no marriage certificate, but have an affidavit indicating we are married customarily which is accepted by the local authorities and my wife gets a dependant visa based on this as am the only one who works. we currently need a marriage certificate urgently. can the Chinese authorities provides us with one on a short notice?