I bought them from someone online. They are copies that cost $72 for the set. I'll see if he will refund the money (less shipping). Oh well, the search continues... The Mercedes Dealer told me that the Navteq CDs are the same for the MCS system as for the Siemens VDO that I have.
Navteq told me that the Mid-Atlantic CD #6 (which is in currently in my Nav unit) is the correct CD for the Siemens VDO system. This means that my Nav unit may be bad. I'm going to take it to the used car dealer on Monday to let them figure out why it doesn't work.
The local Mercedes Benz dealership misinformed me when they said that the 2004.1 MCS CD (specifically CD #8) was supposed to work with my Nav system...