I bought a black 48cc flying horse kit from bike berry(link below) But at the time it was on sale and MUCH cheaper.
http://www.bikeberry.com/gas-engine-kits/gas-engine-kits/flying-horse-silver-angle-fire-48cc-bicycle-engine-kit-1.html
http://www.bikeberry.com/gas-engine-kits/gas-engine-kits/flying-horse-silver-angle-fire-48cc-bicycle-engine-kit-1.html