Look up Eric Sponberg on google. I'd be willing to be he could design you a composit mast that you could build yourself, or at the very least direct you to a good builder for what you need. He's best known for his freestanding, rotating wingmasts, and as such is highly knowlegeable in all things carbon.

Also, weigh your rigging. I bet you could save quite a few pounds by going with synthetic rope rigging instead of wire.