There is a great post on corral.net on how to make them,
corral.net MIL eliminators . I guess you can by them through a mustang place for about $60. The parts for making them are about $7 from Radio Shack. I must have done something wrong with mine though I just threw a 0151 and a 1151 code. I soldered the components into the O2 wires, is this a no no?