Connecting a MIDI keyboard

I have found a nice cheap MIDI keyboard, which I must use with GarageBand. I have an iMic, with which I can plug in my guitar. But this keyboard only has a MIDI output port. Is there a MIDI to USB cable, or MIDI to 3.5mm (iMic) cable that I can use. If so, who makes it, where is it.

Thanks Musical Macers.