There has to be companies like MPBRAKES.COM and Stanless Steel and many others making kits. Check the magazine ads.
However, if they were an option for your car like was suggested, go buy the calipers and rotors from a parts house. I have a parts house I prefer and can send you to that has rock bottom prices and name brand stuff most of the time.
You may need a bracket to mount the calipers to. If that part was available stock then it should be available somewhere new or NOS if you can't find it in a junk yard.
If not, I have my 12 bolt in a machine/speed shop right now and they said they'd have no problem fabbing something up right quick to make it work.
Mine didn't come with rear disc, so I have to figure out what caliper to use. If yours did, your decision is easy ....unless you start reading about the guys putting down the design of them and want to look for better.
I have read some suggestions of using recent Camaro or Corvette calipers, and if you have to get something fabbed up to hold them, you can use any caliper you want almost. Just match the rotor you need to it to keep the bolt pattern you need for your wheels.