I bought some from this mob in Perth -
http://www.fibreglass-resin-sales.com.au/home.html They also have some useful info on their website.
It cost me about $350 to make a 10" tube - actually the tube is about 12" diameter by about 1.2 m long.
I made a two-piece mould using a piece of 12" PVC tube and normal fibreglass and resin, then the actual tube out of carbon and resin. I vacuum-bagged it to get a nice finish and get rid of the excess resin.
The tube weighs about 3 1/2 kilos or so and is single layer woven mat but double layer at the ends for about 200 mm to provide extra stiffness and support for the mirror cell, spider and focusser.