No there is actually no existing List of unreleased Musikladen performances, Although there are a lot of performances never released. It seems that the release of the Musikladen Book end of this year (40th anniversary of Musikladen) will not include such a list like the Beat Club Book do.
That is a very good question Sal, but I dont know there is going to be any answer. They have not been available for some years now and were only available for a few short weeks directly from ARD video.
I believe there were clearance issues at the time which caused the 3 volume box set release to be pulled from sale - I stand corrected and if someone can give us the full story then I am sure we would all like to know - they must have lost a lot of money on these!! I was fortunate enough to order them directly from ARD at the time and I am sure some other contributors here, particularly our European friends, would have done the same.