We have gotten the Suburban / Panel truck rear barn door lock cylinders made so we now offer new
Suburban / Panel truck Ignition, Door & Barn door lock sets all keyed alike so the same key that starts the truck also opens all door locks.
1967-68 ( Original GM octagon key ) Part # 18263431
and
1969-72 ( Original GM square head key can be used on 67-68 also )
Part # 18263444
Found on our lock set pages here
http://www.gmcpauls.com/lock_sets11.htm
I know you'll ask but we do not have these for the Suburban rear hatch / tailgate models.
Paul Jr. @ GMCPauls