I am guessing it's the black bottom cover to the whole unit, correct? I would call Audio Classics, and McIntosh Audio (Tom Manley) to see if they have any lying around. If they don't have any, then you're going to be waiting for one to pop up on Ebay.
FYI the black bottom cover for an MR71 fits the MX110--I got a MX110 with no bottom and snagged a bottom from an MR71 that fits perfectly. Good luck!