Soylent Green

Can anyone help me. I recently purchased a 2005 S55. I received both smart keys with the car but one of the skeleton keys is missing. I went on ebay and got two blanks but they were the wrong ones and would not fit into the key fob. Can anyone point me in the write direction to get a copy of the skeleton key cut. I do have one one of them. The local locksmith said they could probably not cut that key. Can someone give me the correct part number for the skeleton key blank so I can try and get some copies made without paying the dealer $75 per key.
Thanks for your time.