Nothing ventured, nothing gained
I would never be offended to receive such a note. Flattered, actually. It's always nice to know that my boat is desirable.
Having said that, I would also look up the owner in your State registration records and, if the harbormaster would not pass along my note, just write directly to the owner.
Be kind of prepared for a rejection, albeit a polite one.
Sidebar:
Ever since the early 90's, there is a late-80's Islander 34 parked in a marina downstream from PDX. It's one of the "modern" designs and actually a nice looking design. The out-out-state owner has rejected all offers for 20 years. He visits it about once a year and puts another tarp over the boom... and over the rotting mainsail cover. The furling jib is rotted. Small trees grow up from the accumulation of slime at the waterline. Once about a decade ago I walked over to it and (lightly!) laid a hand on a stanchion.... the whole deck surface flexed. This tells me that the coring is long ago rotted out underneath.
It is one sad sad situation.
Last I heard from the harbormaster, the owner still will not even discuss selling it. He does pay the moorage fee every month, though.
At this point it's just a major project with a negative value anyway. Big Sigh....
Best of luck,
Loren
ps: come to Portland and make me an offer......