A while ago there was discussion about the mini banana plugs
used in this system.
On another project at work, we needed some mini banana
plugs, these sure look similar.
I found that Digi-Key stocks some, as part # 314-1403
(black, pack of 10 plugs, for $24)
and jacks 501-1051 (red) 501-1479 (black) and 501-1959
(green) for $2.05 each.
These are roughly 0.1" diameter plugs that squeeze down a
bit when inserted into the sockets.
Not claiming these are the same size as the DEC ones, but my
guess is they could be.
Jon