The Maxum line was shut down in 2009 so I doubt you will find a dealer anywhere that has parts.
The switch is generic and you may try a Bayliner dealer to match it was they are both Brunswick products. Else look on line to match it up.
For the lock try graetlakeskipper or Google boat cabin locks to see if you can find one.
Not sure what you mean by engine plug. Drain plug (blue), Mercruiser part, spark plug, ... Got a picture you can post?
1997 2400 SCR
5.7 Vortec / Bravo 2