I'm looking at a GE wireless PIR sitting on my desk. If it's the same as the 481, a short spring fits over a black nub on the back of the sensor. Looks like darn near anything would work. I'd try a 1/8" diameter, about 3/8" length spring. You could clip or stretch the length and/or crimp or stretch it to fit over the "nub" if it's not exactly right.