I was considering something similar, not sure your location but I was going to talk to this guy. I go to Jacksonville to sail sometimes. Maybe he'd ship one for you
Check your local craigs list too. If it's like mine it has quite a bit of old windsurfing equipment. The majority of it is junk but you might find what you need locally.
What I did was go on Craigslist and look for repetitive ads where people were selling full setups in multiple ads, aka they buy and sell gear. Then I contacted them and asked what kinda old crap pile oldschool masts they had laying around in the impossible to sell pile.
Modern windsurfers aren't buying fiberglass poles so the guy had like 10 to choose from from. Got 4 for 20 bucks each. Make great spinnaker poles.