Here's the situation as I understand it:
There are two known sources that contain a recording of the mono mix.
1. Bootleg VHS copies of the pre-ANH telecine. Distributed at fan conventions and such, it is unknown how many generations down from the original these copies are. Some gaps exist in the audio at the reel changes. (The mono track on the EditDroid DVD is based on one of these bootlegs.) RevBeastly has lent his VHS copy to MeBeJedi to capture; hopefully we'll see some form of electronic copy available to download soon.
2. VHS recording of a UK TV broadcast from the '80s. I dug out a 1st generation recording of this; the tape is worn at the start and it is incomplete; the start and end are missing and there are gaps where the ad-breaks were. I sampled my tape and made it available in two versions: a 50MB MP3 and a 320MB lossless FLAC file.
Whereas it'd be nice to have a cleaner master available, I think you have to assume that this is all that's available at the moment.