Go to an industrial/commercial irrigation supply--they'll have every size and length you could ever want. Check the yellow pages--it may take a few phone calls.

I got a great deal on a 14 ft long 12 or 14" diameter because the end was chipped. So ask to see what they've got in their "scrap" pile. I just sawed off the chipped end to square it up with a hand saw. I also bought end caps. Works great--fits my sails, rudders, wetsuits, life jackets, etc. Good luck.