USM ( University of Southern Maine) in Portland has a fantastic library in an old warehouse building visible from 295.
The 5th floor houses an extensive old map collection. Check the USM website to see about hours and privileges!
Welcome to the University of Southern Maine
When we lived in Gray, Maine, our small library was quite good about interlibrary loans and movies checkouts. It also had a terrific children's section! The Portland downtown library on Congress Ave is terrific, with a very helpful reference staff.
Good luck!