How to buy medical insurance for 70+ who lives outside US now?

My mom has just had an interview of the immigrant process with the US emby in China, she was told to ask the petitioner (me) to buy her a medical insurance from here. I have ask different insurance agents, but most of them don't provide the service for over 65+, also my mom right now is outside of the country, she doesn't have any SSN yet, I can't do anything. Can anyone give me some ideas to solve this insurance issue, so I can reunion with my mom.