You have to write to the Ministry of the Interior, called Misrad Hapanim.
They can give you the information about the date of the marriage, but you might need to prove your identity to them, e.g. that you are mishpachah karov (close family). It may take some time.
I do not have the exact address, as they have many offices, but I recommend that you contact Jerusalem as their office is smaller. Maybe in this case, Haifa might be better, as you think they wre married there.
Good luck to you. Postage is about .80 from the states, but that was before the dollar went down, so ask your local post office. All the Departments/ministry offices are working order, but be prepared to be patient. It takes me about a month to get a response from them, depending what it is, and I live here.
Success to you.