onstar integration

I'm looking to intergrate ONstar into an aftermarket system, in this instance it's a 01 Buick Regal. I've searched for an acutual intergrator piece without luck. So now I'm trying to figure out how to do it manually. I assume there needs to be audio out puts and some sort of activation wire I can use to attach a relay to temporary shutdown the radio and allow the audio to pass through the driver speaker. Any sort of input on this would be much appreaciated, or where I can find a intergration harness. Thanks!!