Alas, it's DPDT, not SPST.
Ooops; the ones in the PDP-11 front panels (/05, /45, /70 and almost
certainly the /40 too) are SPDT, not SPST (typing too fast, in my excitement
that these have finally been found :-).
I looked at the data sheet for the ones you found, and it's actually a sheet
for the whole series, from which it looks virtually certain that the right
ones (both pemanent and momentary contact) can be ordered from C+K. It's just
a matter of working out what the part number would be!
Noel