Kittery Trading Post is a great outdoor outfitter and has an excellent selection of Maine maps and books.
The Candle Shack in Cape Elizabeth is a great place to browse while you wait for your order at The Lobster Shack, a great setting adjacent to the Cape Elizabeth lighthouses, and with waves slapping against the rocks.
Sherman's Books in Boothbay Harbor. Locations also in Freeport, Camden and Bar Harbor.
Moody's Gift Shop in Waldoboro. Right across the parking lot from Moody's Diner, with their renowned pies.
I have warm spot for DeLorme's map store in Yarmouth, as I founded it some 25 years ago. But the store in those early days can't compare to it now. Fantastic selection of maps and guidebooks. While you're there, enjoy Eartha, the world's largest revolving and rotating globe.
Gift shop at Foster's Clambake in York.
The Smiling Cow in Camden. There is another location is in Boothbay Harbor.
You'll find the map in more than fifty other gift and book shops along the coast, two of which will be featured in future posts, and if you need it before you visit Maine, it's available on amazon.