My first step would be E-bay (and the US specific "for sale" sites). Mast won't need to be an exact duplicate - but make sure you keep "your" mast fittings, just to make sure all is good
Not sure from your description where / what the damage is (US terminology, I think
) - but just to mention it is possible to Sleave
a mast......which is basically joining two bits of mast together with an insert. Never done one
but seems that the lower the join the better.
And FWIW, my boat (and her 100 odd sisterships) have sleeved masts (3 foot? above deck) - mine has been good for 40 years so far
and I have not heard of any failures........