I have a 1965 Mustang. It is almost certainly the upper control arms. As far as parts for your car, they can be bought in lots of places. NationalPartsDepot.com is where I buy most of the things I need for my Mustang. There is also California
Mustang, Johns Mustang, Virigina Mustang...lots of places. You can buy virtually any part you need for that car without going though a mechanic and paying a markup. The parts are new reproductions, mostly very good quality. If you want some help with your technical questions and want to hang out with a bunch of other classic Mustang owners, go to http://www.mustangforums.com/forum/classic-mustangs-16/
That is the Classics section of Mustang Forums. I am a member there and the members love to help other people out with advice. We would be glad to have you.