I have a perfectly fine older AVH-P6500DVD with the older AVIC 80DVD for GPS.  Of course maps are no longer supported.  is there any aftermarket GPS add-on that can replace the AVIC 80DVD?

You can easily upgrade to 2012 map disc, you just need to copy certain folders from your old map disc to a memory card (max size 8gb) & this will allow you to run newer discs in your old unit.