RJ45 splitters?

["Ian" <ian@xxxxxxxxxxxxxxxxxxxxxxxx>]

I'm looking for a splitter that lets me plug four (and a separate one for
two!) RJ45 cables into a single RJ45 socket, so basically, one plug, four
sockets, all commoned together.

I picked up a couple to use for plugging a bunch of stuff onto an ISDN bus
last time I was in the netherlands from this amazing little cave-like
electronics shop full of rare connectors and cables, somewhere down an
amsterdam backstreet... As for the UK, they appear incredibly hard to track
down!!

Any leads?

Ian.