If ur like me and cant be bothered reading thru all those sites to find an answer.. then read this..
You need to take the HU out of where its placed and take a look at the back. They are generally listed, and new cars generally do have outputs for RCA.
If there are none, buy a car from a company that thinks about ur needs
But seriously.. I dont know if there is any alternate way to do it unless u open the HU and wire it all urself. Just buy a decent HU, most of the standard ones are crap anyways.