The patent on them expired about 3 years ago, I'm surprised there aren't more off-brand ones about. I was thinking of sending one off to a factory in China to have it reverse engineered and a bunch of them made with my own name on them. That's very much a pipedream though. I have the 'lite' version that came on a Fernandes Mustang clone. It's a double-coil - essentially a single-coil and the sustainer coil. The coil that makes sound is pretty anemic - so i was thinking of upgrading that part of it. But make no mistake they are LOADS of fun and you ARE missing out. I'm about to sell that same guitar but I'm gonna take out the sustainer first because from my cold, dead hands.
But in principle they're not that difficult to make. They're only 120 winds worth, so you could do that much by hand. Count 20 winds in your head - then glue gun - repeat another 5 times. Then run the 'live' pickups through a pre-amp and whatever a "ruby" is through to the sustainer. From what I've read.