Can I search for mom's bank accounts using her social security number?

She was a hoarder and keep paperwork from years ago. I still haven't gone through all of the papers. She also had stocks There is a company that will search for me. But charges $99. I can send death certificate to each possible bank and stock place. Don't want to waste death certificates and time on places that probably mom doesn't have current account at. Is it possible for me to do my own search? Or do professionals have access that I can't get?