I have a few of these Model M cables (original PS/2 cables) that I have taken off Ms I converted. I have 2 listed on eBay right now, but I may list more later. great if you bought a model M and didn't get the cable with it.
http://www.ebay.com/itm/331445627950Price is $10 + $4.50 shipping, but if you PM me, I will sell them directly for $12 shipped in the USA. (not a huge discount, but something anyway)
-Ezra