Nitro has them listed.. $289 for the buggy engine $399 for the on road engine.
http://www.nitrohouse.com/engines,_ninja.htm
They look good! I hope they work out well for ya.
-- John --
1:1.. 01 Z28 Camaro A4 Sure.. its stock.
1:8's.. K3, Inferno GT, and a straight line beater car
1:18.. RC18t Mamba and 3s lipo