You would only see Boardwalk buses at the theme parks and Downtown Disney, as BW is also a resort. There are no resort-to-resort buses. Coming from say, POP, you would take a bus to MGM and board a boat to BW (that would be my preferred route); or take an AK or MK bus and transfer from there to a BW bus.
Or better yet, book a room there (or one of the other neighboring Epcot resorts) some time. It's nice!