I have had real good results with the round head 48 cc motor.
I saw one on ebay from this seller eBay Feedback Profile for rawpowerusa
It came from here RAW 48/50cc bicycle engine kits EPA Certified
I bought the motor on 10-14-08.
On 10-15-08 they shipped the motor and emailed me a tracking #.
Got the motor on 10-21-08 from FedEx.