where can i find the engines

I had a problem with the engine: I've bought the 911 E from the used car dealer, and in my garage, the car car could not work cause the cylinder head was missing. I've tried to find it in the shop and unable to find one for this car. With the "testme" cheat, I took another 911 E, wich was running perfect. It seems that the engine with his components is made of one block...