Somebody Came
I recently replaced several of the marelon through hull fittings on Bacchus, H54 - 22. I found Forespar 253 Series Marelon Mushroom fittings at Defender Marine. They had a number of different sizes and were long enough to go through the hull. Note these were above the waterline fittings, not below the water line.
Good Luck
Scott Johnson
SV Bacchus
H54-22