robsant,
For new, try your dealer, or do a google search for mercedes phone parts. One supplier is at
Mercedes Bluetooth, but I don't know how prices compare to the dealer. Other than that, it's ebay.
One additional factor - MB has announced "End-Of-Life" for some of the kits for older models (this should not affect your '05) - so if owners of older cars try to order the parts as a whole kit, they may be told they are no longer available. However, the individual components of the kits are still available - they just may not all be packaged together. The part numbers may have changed from a "BQ" (kit) part number to an "A" (component) part number.
