I got a key made for my W126 about 6 months ago and my dealer got it from a Mercedes place in Baltimore. $20. Two years ago when I got a R107 key made, they did it on premises, but that key machine doesn't work anymore.
1988 560SL Black/Palomino
1988 300SEL Black Pearl/Burgandy
1984 500SEC Anthracite Grey/Palomino