Tracing a marriage certificate

My mother got married in Japan in the late 60's-early 70's to a non-Japanese, both did not live in Japan they were just tourists who came to Japan from a neighbouring country to be married.
Is there a way to trace the marriage and get a copy of some sort of certificate, I'm quite sure the marriage was registered as they would have needed a proof of marriage.

So far I know tourist cannot marry under Japanese law without a one being Japanese or living in Japan.
So if two foreigners want to marry in Japan one has to live in Japan.
Is the marriage not a symbolic marriage and your parents had to show proof to arrange a second marriage (party) in Japan?

even if the information was registered, you have to know where it was registered.
when you can't specify the place, you can't do anything.

So both were non-Japanese, and neither lived in Japan at the time? As far as I know, two non-Japanese people can get married in Japan without either of them living here in Japan (at least in Tokyo, and as far as I know, more recently).

You could first check with the embassy/consulate of either your mother or the spouse in Japan to see if the couple later reported the Japan-law-based marriage to the respective country after-the-fact (which they might have or might not have done).

If not, you would at least need the city/ward where they got married.
And even if you find it, the only type of document the Japanese authorities provide is a paper certifying that they accepted the marriage report at the city hall, not a paper called gmarriage certificate.h (Since neither of the couple is Japanese, there is no gkosekih (family register) to enter their marriage into.)

Thank you all.
I'm pretty sure they married in Tokyo and as far as a marriage certificate goes, at this point any document I can get to prove the marriage took place would be a big help.
I'll try the embassies, though I doubt they keep records of such matters for that many years.

Marriage certification is registered with the city hall where they register their marriage. Which I do not think is possible for two foreigners with a temperately visa unless one of your parents have lived in Japan, with a fix address and are registered at the local government.

You may say you are sure they married in Japan but there is a law about marriage in Japan and requirements.

Again you better to check if there is a marriage certification register in the city were your parents are living or lived before. If they married in Japan than they also had to register their marriage with your parents local city hall. (depending on your laws)

It may indeed be good to contact to embassy of your country in Japan, to confirm if they are married there. If they married at the embassy of your country they are not married with Japanese law and therefore not married in Japan. If your parents married at your country embassy in Japan than they are married with your country law and all information should be in your country.

Maybe your are mixing the information which you think that they are married in Japan, but again this is not possible for temporary visitors. If marriage was possible without living in Japan than many people would marriage also in Japan on a temporary visa.