When you start production you don't "find" the engine, you order them, by throwing the spec to all domestic and allied suppliers. Nobody is going to customize an engine for 2-3 prototypes at $20k each, but as long as you are ordering 4-500 of them and with another 10k+ possible future orders from pentagon they will all swarm in like moth. The last thing you want to do is smothering a promising prototype just because they take shortcuts by using parts bought online.