MIDI gear will only respond to the channel its set to. So you could run up to 16 pieces of gear off one MIDI output. The devices just throw out the other information. Therefore, there is no need to split the cable into different channels. A splitter will simply send the signals to all devices, you just need to make sure each piece is set to its own MIDI channel.
I've bought patchbays and spitters used as they are a bit overpriced for what they do, but you can still find them new. I don't know if they make plain midi patchbays anymore, usually you have to buy a 8x8 midi interface for your computer, but they also have the ability to work as a patchbay too.
1 in, 4 out splitter
http://www.musiciansfriend.com/product/ ... sku=702504
old patchbay example on ebay
http://cgi.ebay.com/ROLAND-A880-MIDI-PA ... dZViewItem