Nutone made those units for years and years. I don't know what year your boat is, but it could be a Model 220 or 221 or Model 250 or 251. The sticker may be underneath if you pull it out. Parts are usually available on eBay as are whole units.
Replacement is sometimes done with one of these. The cut out dimensions are the same and I think there is an adapter to use Nutone accessories, if I remember it is free for the asking from the manufacturer.
https://www.thekitchenprep.com/
I've only seen them for sale direct from the manufacturer and on eBay.
On the flip side, I think it is 1000w vs 650w for the NuTone, so do check that the wiring and breaker are up to it. I suspect it'll be fine, but it does need to be checked.
Also, I am going from memory, so don't trust anything here-- verify it.