There are scanned PDFs of the complete proceedings from the first two workshops (UBC 1974, UQV 1975) in the Hathi Trust digital library.
Don Boettner had hard copies of the proceedings for all of the MTS workshops, "almost all in their original binders". He also had a set of "preliminary notes" for the Intersystem Workshop '88 held at UM. Don didn't have proceedings and we aren't sure if there were proceedings for the 1994 Community Workshop in Edinburgh. Don did have Kari Gluski's 6 July 1994 trip report from the Edinburgh workshop.
Don gave his copies of the proceedings and related materials to me (Jeff Ogden) on May 13, 2014. The goal was to scan some or all of the proceedings to make PDF and then give the physical proceedings to U-M's Bentley Historical Library and the PDFs to the Bentley for storage in U-M's Deep Blue Digital Archive and to Bitsavers (if they will take them).
As of 24 June 2014 there were scanned PDFs of the table of contents (schedule, list of papers, list of attendees) from all of the proceedings in the "Documents section" of the MTS Archive (this site) except for the final 1994 Community Workshop held in Edinburgh. In September 2014 work started to scan the full proceedings. As of 6 January 2015 the full proceedings for all eighteen workshops had been scanned, OCRed, and made available online. Check in the Documents section of this web site for a list with links to the PDFs.
At the Bentley Historical Library …
... the Computing Center Records section (boxes 7, 28 and 29) contain the following:
1978 (4 expandable folders)
1986-1987 (1 folder and 2 expandable folders)
1988 (2 folders)
1988 Workshop Proceedings, "1st Intersystem Workshop, 14th MTS Workshop" (5 VHS videotapes)
1989-1993 (3 folders and 2 expandable folders)
Not sure exactly what is included in the above items and in particular not sure if proceedings are included.
... the "Michael T. Alexander papers" collection (Box 3) contains the following: