This link gives instructions on how to install a font hack for the DX.
https://sites.google.com/a/etccreati...works/dx-fonts
It also includes several fonts, but I didn't see a dark or bold font listed, unless I missed it.
ETA: Link to this discussion on the Kindleboards - I meant to include that, duh.
http://www.kindleboards.com/index.php?topic=11043.0