I am sort of in the same boat, old(er) iMac, so no USB 3.0 (albeit I do have thunderbolt) and I was looking for a CF card reader, FireWire 800 preferable. I heard that the company who makes the circuit boards for FireWire (they apparent supplied everyone!) when into liquidation, and that's why the availability dried up. No one could be bothered to look into making them again, as USB 3.0 was pretty mainstream.
However, as I stated, I am on a mac... I am running Mountain lion, and I can confirm, that a little German company called DeLOCK make a CF FireWire 800 card ready, that works very well. I have been using it for about a year now, and very happy with it.
I hope this helps