No video preservation that I know of has the full 70mm audio, since no preservation has the 70mm video. Even then, we’d be talking mono tracks from in-theatre recordings or reconstructed from the 8mm digest. It’d be pretty ugly, although maybe possible if you wanted mismatched audio badly enough.
Didn’t morgands1 preserve a tape recording of The Empire Strikes Back from a 70mm showing in 1980?
EDIT: A recording of the audio, not the video.
That’s what I meant by a mono in-theatre recording. Yes, it’s technically possible, but it’s a pretty odd request. The 35mm video was never shown with 70mm audio, so it wouldn’t be so much a preservation as a fan-edit. And the result wouldn’t sound very good either, so I suppose that’s why nobody’s jumped on it: i.e. it’s a custom version of Empire that’s not the least bit authentic and also sounds bad.