I've changed out several radios in the past, as I have a lot of old toys. I hate butchering wiring, or finding wiring that has been...by a P.O. What I have done in the past when I could not get an adapter kit was go to the wrecker and find a radio that is damaged, or low end, something nobody would really want, that's installed in the same car, and clip the connectors off of the radio about 2" back from the connectors, then I simply solder and shrink sleeve the wiring of the new unit to the old connector, and TAH-DAH! If your new radio comes with a connector of its own and you don't want to cut that one either, get an adapter kit for whatever, that fits your radio, cut the vehicle end off of the adapter and solder the wreecking yard connector to that, and VOILA! instant adapter kit. Simple and effective, best part is that everything can still be returned to original if ever you wanted.
-Chris