If you are talking about the chrome rails that are mounted length wise and a few inches from the sides (not drip rails along the far left and right sides), they are both available through the dealer at roughly $250 each. The part numbers are:

A1076980381 Garnish Molding Left

A1076980481 Garnish Molding Right

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All the best,

J. P. Mose
1968 250SL
1970 280SE 3.5 Cabrio
1987 560SL
1990 560SEL