There is a guy in cherry valley about 20 miles from riverside that sells them. His name is Rick, his company is American gas bikes. I believe he has a facebook page. There are quite a few on craigslist also.
We never did but there are a bunch of bikes popping up in riverside. I run a vintage bike ride on Facebook "Riverside Vintage Bicycle Club" and was thinking about starting a Motorbike one too. I sold my old bike some time ago and I'm picking up my new one this week. I'll shoot you my info in a private message. If you have a Facebook, join the vintage bicycle club too.