try,
michaelgraves.com

i fuckin cannot believe it.. i was being silly as usual but my made up link actually came up when i copy pasted after posting it.
many products by graves. including restaurant art. the guy is full service. sorry no prismacolor.

I like Chartpak better for working on trace - they show less overlapping areas. This is the best place by far to buy them based on price: DickBlick.

been using Copic sketch markers recently and they kick Prismacolor's ass. a bit more expensive though, but they are refillable and have replacable nibs. check em out at copicmarker.com

I love Prismacolors but they run out of ink so fast. My vote goes with Chartpak.

Try ebay, seriously. They have brand new sets for next to nothing.