Bangor Ski Rack is the only one, and it's 1.5 hours from Brunswick and then about the same to the Kennebec from Bangor. Not very convenient.
Ski Rack Sports Bangor Maine Kayaks, Bikes, Skiis, Snowboards, Camping, Outdoor Gear
If you're jonesing, you're welcome to use my old Dagger Freefall LT or Estanguet slalom C-1, both of which are at my in-laws' house in Freeport (one town south of Brunswick). My father-in-law has a Necky Jive, Asylum squirt boat low cut for 150lbs, and a Perception Corsica S that I'm sure he'd let you use (maybe not the Asylum, as that's his baby). They're also in South Freeport. My father has a Prijon T-Canyon in Boothbay Harbor.
Shoot me a PM if any of these interest you. Unfortunately, Maine is my repository for boats I no longer use.
There's also a few people who might lend you a boat, if you want to go that route.
You might also try posting on the squirt boaters' message board, as there are Mainers who check that regularly and might be willing to lend you an extra plastic boat and gear.
Good luck and let me know if I can help.