Unfortunately West Marine close the Woburn and Seabrook Store #2.
Seabrook #1 is open. The Seabrook store is marine maintenance while the Portsmouth store is more clothing, fishing and electronics.
The Portland store is the biggest one that I know of and it is a hike!
I've been having good luck getting used parts from M&M salvage in Meredith and Ebay.
Irwin Marine has the largest ship store that I know of on the lake.