We used Carbon Fiber in the construction of our ramps last year. It turned out that we rarely used our ramps, but still it was good to learn how to work with the stuff.
You can easily find plain CF cloth in small quantities all over the web...
http://www.aircraftspruce.com/menus/cm/carbonfiber.html
is one such place.
They also have a variety of foam core materials. We used the small cell styrofoam, 1/2" thick, inside the panels and embeded hardwood mounting points for our kickstand and hinges. We also added some heavy fiberglass cross spars as well. The ramps could probably hold hundreds of pounds yet weighed just a few pounds.
as for prepreg stuff... sorry not much help there.