Kensington 7-in-1 Media Card Reader for Express Card Slot:
http://us.kensington.com/html/12631.html
Price: $39.99
Doesn't support CompactFlash (CF)
I think the reasoning behind this is because the card reader I posted fits flush with the notebook edge.
Compact Flash cards are a bit taller, therefore the reader needs to be taller, and may not be able to fit flush with the edge and need to stick out a bit. This could be the reason you are hard-pressed to find an ExpressCard slot reader that supports both formats.