I don't think there are many good used ones around. It wasn't one of Ford's "better ideas" If you ignore it they can fall apart and you'll lose the steering. A lot of good cars were junked because of this crappy setup.
The 69 Torino shares a lot of mechanical parts with the Mustang.You can get all the parts to rebuild the slave cylinder from most Mustang parts dealers.But they are wicked expensive.
I know a guy who tossed the cylinder and replaced it with the non- power steering tie rod. Then he put in a power steering box from an Isuzu Trooper and hooked the pump to it. He said it was almost a bolt on. one bolt hole lined up with the frame and he redrilled two bolt holes. I drove the car when I painted it and the power steering worked great.
AL