yes there are applications that can do it - you need one of the mouse/keyboard keyboards that are available and a piece of software called 'Hubbi's MIDI Loopback Adapter' - which basically create 4 virtual midi in and outs and lets you set the routing of them to real ports.

OR you could just buy a keyboard - you can pick up a midi capable keyboard for about £30 on ebay these days, and a USB MIDI interface you can probably get for £10-£15

Hope this helps,
Chris