Welcome to the forums, Jim
Unfortunately, I don't think you'll be able to penpal with a maiko. They have incredibly rigorous schedules (2 days off a month is the standard, I think); early mornings and late nights. Other than the obvious time issue, their okiya and ochaya are private establishments and their world has an etiquette all its own, which more than likely wouldn't allow such a thing.
But, you can follow the Japanese bloggers and other social media accounts and communicate with their world that way. Do you know any Japanese? Tell us about your interest in the geisha world
new faces are rare here