Many of our online bike stores offer frames sans forks as well. As you said picking the king of fork you want when building a bike from the frame up. You have to pick the bars, stem, seatpost, saddle, pedals, Crankset, Chainring, bottom bracket, and wheels. And many of the frames on E-bay are the same. Often you will find they are new when you click on the frame. If they aren't they may as you suggest come from a damaged bike but they could just as easily have donated their parts to a new frame for the owner. read the discription and the rating for the seller well and decide if it is a risk worth taking.