A forum member, Greazzer, was just looking for a w115 intake manifold, so you might contact him for leads. I think he got a bunch of offers.

On car-part.com, there are several listed. The going rate is around $75, although one place in San Jose had one for $65.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).