http://www.thermaflo.com/heatsinks.shtml
Pick a size, any size. Need a long skinny job to cover a bunch of MOSFETs in 1 sweep? This has to be the place. They will make a custom one for you. Those cross cut jobs sure have a lot of surface area. Let's say you have a northbride with a chunk of aluminum 40 * 40 * 6 and not much room. Suppose you opt to glue down in it's place a cross cut 50 * 50 * 12. Think you might increase the surface area a tad? Artic Silver has a thermal epoxy that totally non-conductive (see elsewhere).
I'm just letting people know I found this. I suppose you could ask for samples.
I have made no purchases, but did note they have no minimum order. If you look at this page:http://www.thermaflo.com/extrude.shtml
The V shaped unit pictured on the right is measured in inches and has to be the heatsink used in Plinius amps.