Hi James,
I'm not in a position to sponsor you. However, here are some points worth thinking about.
1) What type of sponsorship are you after? Funding or equipment? If funding, for what purpose - travel, equipment, making a living?
2) Here's the question you need to think about from the other side of the fence... what are your sponsors going to get in return? There aren't many companies out there that will fund people for the sake of doing something nice. Generally they're going to want publicity in return. Your role is to articulate exactly what publicity they are going to get and what demographic you are going to be targeting.
Here's an example:
You have a blog - maybe not just about you windsurfing, but also about windsurfing in general - that gets loads of internet traffic.
You have your own website
You regularly make movies of windsurfing and post them on youtube that get loads of traffic
You have a vehicle that you're prepared to coat with the stickers of your sponsor
That vehicle gets parked somewhere where people who might be interested in the products of your sponsor see it
You get coverage in the general / windsurfing press.
You create your own photography / movie production / clothing brand company
It's hard yards - I know a lot of sailors who can do some properly mad tricks (Air Funnell -
-, Toads, etc) who aren't sponsored. You've really got to create a business case that's going to say "if you sponsor me this is the number of people who might be interested in your company that's going to hear about you as a result".
On top of everything, I suggest you start freestyling as soon as possible (if you haven;t already). Wave sailing gets a lot of coverage in the windsurfing world compared to everything else (I think anyway - just look at the magazine covers), and the good wavesailors these days are as much freestylers as they are wavesailors. Learn as many of the maddest tricks you can - the best guy at the beach stands the best chance of getting sponsored.
Above all.... good luck.
As examples of people to look at, try the following:
http://www.k718.co.uk/Home.html - John Palmer, great windsurfer who worked at Club Vass and Dahab for several seasons.
www.lauretreboux.com/ - a good example of a well-run windsurfing site