There were two styles of the Mustang. One styly was a simple design semilar to the Pearson Hunter. The other had "integral stabalizers" or "horns" made into the riser. I prefer hte second.
Your best source for any old collectible bows is ebay. Just go into the main page and type in Ben Pearson. Old Ben Pearson bows are about the most under rated, under valued bows out there. They are solid shooters and it is not uncommon to pick them up for $50-$100. Sometimes even less.