Quite simply I am looking for places that sell a dual-tuner (able to
record two different channels at once), Tivo Box (dvr) that can be
used with digital cable.  I know Hughes makes one for Directv but I
have yet to find one for digital cable.  A) is there such a unit made?
 B) can you provide me with links from where I can buy them?

I thought I had one for you:
http://www.sciatl.com/consumers/Exp8000.htm

But, unfortunately, it's not available at retail in the United States
unless obtained through certain cable systems. Perhaps some other
Researcher could find one available on the gray market.

It looks like a cool set. Not only can you record two shows at once,
you can play back a recorded show at the same time!

Time Warner Cable in NY offers one for its digital customers (maybe it
does in other areas as well), but if you read assorted user's groups
and reviews, the machine has a lot of problems, compared to TiVo.