... anyone know of ~30mm lowering springs available state-side?

I've seen them advertised in Europe for the Mercedes W116 for Euro 300.00

ie,
Eibachs (for W126 but these should fit the W116):
Eibach / Pro Kit Lowering Springs / Mercedes S-Class (80>91) W126 / Euro Performance Car Parts

and the

H&Rs for the W116:
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For my 1979 300SD, bought a set of H&R Sport springs for the W126 (code 29554) from Tirerack today.

Will install when the 8x16 pentas are refinished and new rubber (Michelin Pilots) installed. Bilstein HDs and new bearings (especially!) making a tremendous ride difference already.

Will report in a couple of weeks the comparison.