Hoping that someone can help here – a friend requires a new freehub for a non series shimano hub (FH-RM65) that came with a Cannondale F4. I've done a web search and it tells me I need the part number Y3CT98040 but I can't find this part for sale anywhere. Can anyone advise me which shimano freehub(s) are compatible with this rear hub as the distributor doesn't know.

Should be the same as an RM60 body which is part number 3CF 9804

FH-RM65 diagram

FH-RM60 diagram

So the importer does know 😉

Thanks for the confirmation of this – it still doesn't help with what freehub to order online that will fit this hub. The importer didn't seem to know either:
Their reply

Unfortunately we do not range the particular Shimano freehub body you require. It appears to be a Shimano Original Equipment part spec'd by the bicycle manufacturer directly from Shimano.
We would suggest contacting your nearest bicycle brand dealer, they should be able to help you locate a replacement freehub for your bike.

but with the part number you suggested I've found someone that sells it – many thanks!
Shimano non series freehub

I will find out who sent that reply and give them the details I gave you so that they know in future.

Ok – no bother – I don't want to get anyone in trouble. I'm glad you could help though.