Obviously all the audio is up at https://www.mljtrust.org/sermons/ and administered by the MLJ Trust.
Apparently all of the sermons were transcribed and printed in the Westminster Record, but I could not find any old sources of that newsletter. 22 sermons are available here: http://www.sermonindex.net/modules/articles/index.php?view=category&cid=29
Anyway, I have a feeling if Logos were to partner with the MLJ Trust to transcribe his 1600 sermons (or dig up old Westminster Record printings) that this resource would sell like hotcakes.
I'd love to buy an MLJ Sermon Archive for Logos.