I am not aware of any IP trademark or copyright lawyers in Maine who do pro bono work. None of the Volunteer Lawyers Project attorneys are listed as doing IP work, either. But there is a group out of Boston that focuses on providing pro bono legal IP patent assistance that may of use despite it not being directly in the trademark or copyright areas of IP law.

There are many things to learn and some of what this group offers will provide great educational background: https://artsandbusinesscouncil.org/patent-pro-bono-program/