I often want to contact people about old research, but they have changed institutions or retired. I can usually find their most recent address, but no working p

I often want to contact people about old research, but they have changed institutions or retired. I can usually find their most recent address, but no working phone number, and they usually have no social media presence. It is ironic that the fallback method for cold-contacting people in the Internet age has to be snail mail.