That's too bad that they don't have the parts. I think I've got a 15 at home that needs work, somewhere.
The Aircraft Spruce headbands won't really work on the Lightspeed headsets. When mine broke, I was just climbing out (in a PB4Y, a B24, lots of vibration and shaking going on), and the headset simply failed. The band over the top popped, letting the earcup fall off one side, and the rest of the headset fall off the other.
I had a roll of electrical tape in my flight suit. I taped the headband back together and sent it to Lightspeed shortly thereafter, as previously described.
Mostly now I use a Bose QC-15 for the headset portion, and a U-fly-mic for the microphone. It folds up, doesn't take much room in the flight bag, and I can use it for lots of other things (like travel) with a little MP3 player. It's got excellent accoustics, and has the same electronics as the A20 (so far as the ears portion goes...the mic is different, of course). I'm getting set to order another as a spare.