I need to make some prototype heat spreaders out of a thermally conductive polymer. I want 2.5" x 3.5" x 1.25" (or there about) blocks that I can then machine

The company that makes the material will sell a compression molded block at an outrageous price with a significant lead time. I get the impression that they don't want to do it. I'm also concerned that the compression molded material will be porous, which is unacceptable for my application.

I can get pellets shipped the next day at a resonable price.

Are there any companies that do this sort of thing, i.e. make standard sized injection molded blocks without the cost of having a mold made?

Any info would be appreciated.