Name change process for nris/ocis

Hello, I used to live in Tamilnadu and now live overseas. I am a foreign national and have an OCI card. When I lived in India, I had an official name, say, Gayatri. My "home" name was different, say, Ganga. All my official docs - SSLC certificate, college degree certificate, Indian passport, foreign passport, OCI card, etc. - all have the name Gayatri. However, after my marriage, we purchased several financial assets such as shares and bonds using my home name Ganga. So, all my documents were in the official name Gayatri, but several shares and bonds are in the name Ganga. This was all in the pre-KYC days, of course (1980s, 1990s) - so, no broking firm questioned this. Some of them are in my name only, and some are in my husband's and my name. Now, when I want to convert all the financial assets to my official name Gayatri and demat them, I am stuck. All the share registrars want me to get a gazette notification from the state of Tamilnadu (my home state before I moved overseas) stating that Gayatri and Ganga are the same person. However, how do I get the Tamilnadu govt to issue a gazette notice that my old and new names are the same when I don't have any documentation in the old name? I do have copies of share certificates in my and my husband's name, and I have my old wedding invitation, which has both names on it. But I have no official documentation stating that I was the same Ganga who is also Gayatri. Looking forward to guidance.