Front Drum brake troubles on a 1964 Dart

Hello I bought a 1964 Dart convertible where every time I hit the brakes after about 10 minutes on the highway it starts vibrating violently. The previous owner said that he had just got new drums for it. I think he sold the car because the new drum brakes were warped. Does anybody know a good place to buy good new or NOS drums? Any good brands? I read someplace that the newer drums aren't as thick and warp easily.

Any help would be greatly appreciated!
thanks,
-Paul