Jameco electronics is a place that's got the parts and is available by the web. (www.jameco.com)

Something you should do is tie the grounding jacket of the plug to the designated ground pins. Using that outer jacket as a ground is sometimes unreliable -- my adapter suffered gradually worsening glitches from it until I added a jumper there.

I'd also consider adding an external power supply through the appropriate pins instead of using the transmitter's own batteries. (I notices that the Tom's site that Askalon referred to uses external power. It's a good idea I've been meaning to do for mine but haven't gotten around to.)