Well, I had a private e-mail telling me that Porter's (a US camera shop)
sell such things.
That would be great except that they won't supply outside the US unless I
pay with a cheque or bank draft in US$. This is too much hassle and involves
quite high bank fees. Sheeesh! Is this the 21st century or what? I've bought
lots of things from the US with a credit card, why can't Porters do that?

I believe Paramount will custom make a cable with multiple syncs, for
different species of plugs (IE: sunpak or vivitar or other proprietary sync
plug, and say a household HH male so you can plug a long extention cord to
the monolight, or maybe you need one of those microphone type jacks for it.)
you can do a search for them or go to the z-prophoto mailing list at
yahoogroups.com where there are hundreds of handy links to vendors and
professional suppliers.

However I see those little adapters in many camera shops, even consumer
stores in the malls, often on a rack.   they tend to be a pain cause you
have so many things to come loose.   I even have one of those 4 way pc
things you are asking about.

Are you trying to fire off a bunch of small shoe flash?   Most monolights
will take a household type plug so you can use a hardware extention cord and
one pc to HH cord.  There are HH male to PC you can then plug your shoe
flash into the extention cord.  then you have polarity issues, use some
marker or nail polish to put a dot on each side so you can replicate which
way the plug is supposed to be or you will have problems with rapid fire or
no fire.