How To Instal After Market Stereo In 87 Chevy Suburban With Factory Wires Missing?

I have recently received an 87 Chevy Sub. and I want to install my own radio, but someone has removed the original wiring to the radio, or so it seems. Can somebody tell me how to find out if the wires are gone permanently or what to do in the case that they have been removed and are long gone.

Thank you...