Look at the CNCRouterParts stuff. It's not exactly what you're talking about but for not a lot more money it might be a wiser direction.
You can also look into using Joe's CNC's rail system. It's another popular, but cost effective machine design.
One other thing to throw out would be using something like these: Glacern Machine Tools - Linear Rails and Bearings. Definitely more costly, but since you're making money from the CNC machine, it would probably be wise to design a better machine.
Otherwise: Bearing Trials~Solsylva CNC Plans Should be what you're looking for as far as using black pipe.