I'd give Bacon Marine Supplies in Annapolis a call. They have warehouse of used stuff on consignment that makes the warehouse at the end of Raiders of the LostArc look like a coat closet. There is a whole whisker/spinnaker pole section that must have 50 poles. One might be carbon.
You could also give Jay at AnnapolisRigging a call and see if he has one or some leads. He has a ton of old stuff behind his building and he works on dozens of raceboats.
I still have the 15-27' forespar adjustable whisker pole here in AC. I'm told it can be repaired for a couple hundred and you'd have a 5k pole. Or u could cut out what u need. It's 4-5" dia
Chris chris4911@comcast.net
There's a derelict 2 masted cat ketch ±24' that appears abandoned post Irma. One of the masts is on deck broken near base. The boat is here 25.747701, -80.144024.
I will leave a note next time I kayak around it if you're interested.
You may have already decided against laying up your own tube, but if you haven't, rather than using ordinary cf cloth as I think was suggested, you can find woven cf sleeves that make the job a lot easier. Or kevlar, or a blend of the two.
Or you could get a tapered Al flagpole probably at a reasonable price.