The UMich guys have made available images of tapes from many MTS releases. Not all releases are complete. They've also provided a built system of D6.0 (1986? -87?) with all the further changes it was running just before shutdown in the 90s. (No tape images for this version yet.)
You may want to look at: http://archive.michigan-terminal-system.org/ ASMH is a licensed program product, so they can't make it available. MTS used a fairly heavily modified version of it. A lot of other languages are included, though. There's a list on the above web site somewhere of the license status of many things. Source is included in the tapes. If the SHOW bits to which you refer were shared amongst the consortium, and predate the release of D6.0, they're quite likely in there somewhere. IIRC the copy of the MTS manuals on bitsavers were actually freshly generated in the last few years, so the thing might be referenced there. De