There's plenty of cobra calipers out there. You should be able to find a set.
99-04 GT brakes are a good alternative. Calipers, lines and rotors can sometimes be had for $100. They offer good clamping power. In terms of how they compare to cobra brakes, think of it like drag brakes vs road race brakes. In a one time stopping event, both would prob be close to equal, however start braking repeatedly and the larger, more massive cobra brakes will outperform due to ability to dissipate more heat.
13" brakes do look better in 17" rims though.
Out back, run whatever you want. Drums, GT brakes. Cobra brakes. You'll prob never notice a difference really.