cheapest source of heatsink/thermal pads?

Any silicone thermal pad sucks. I've just measured some in TO-220 housing. Regardless which I've used (Bergquist, Fischer and some other) they have a thermal resistance of 2K/W and more.

When I changed to the good old micas and using thermal grease I could simply obtain half of the thermal resistance. In other words: When using micas you can use a smaller heatsink.