There is: www.classicmustang.com
That should get you what you need for sure
Hope this helps you out!
Try e-bay, and also type in 65 mustang on your browser and I'm sure you will come up with parts places galore for your mustang, also as the one fellow said the falcon and also the mercury comet have a lot of interchangable parts with the mustang. Check with your local junkyards also as sometimes they have old cars stored in the back of their lots.