Knowing what frame the mech hanger came off is one thing, but there all 100's of different models of hangers out there all different shapes. And lots of them change which hanger they use oon a certain model and make of frame each year..... so it can be crazy to find one.
One of the best things to do, is go to your local bike shop with the hanger, and they can either match up with a current one in stock, or match up to what each shop should have, being a large hanger poster with loads different designs.
But hopefully tarty will help you out. If not try this.
Matt