So a couple days ago my SC rolled into the middle of a parking lot out of it's parking spot.
I normally leave the parking brake on with the car in neutral and when i ran out to my car (no one it hit or anything thank god) the parking brake was still up and I was a little baffled about how it managed to roll out into the lot.
I double checked the parking brake and it was working fine, so i moved it and now whenever i park it I leave it in gear.

Anyways, my question, for the Lexus SC, with stock brakes, does the parking brake have it's own rotor and pads or is it just integrated in with the foot brake?

 

It uses a drum-in-hat system. The center of the rear rotors are recessed, and inside lies a springing mechanism that pushes parking brake shoes towards the rotor, grasping it. It seems your parking brake shoes are worn out.

Even if you had brand new parking brake shoes, you should still park you car using the parking brake, as well as leaving it in 1st gear.