I can only speak for the Wouxun KG-935G Plus (since my KG-UV9D Mate is not GMRS only), but I seem to be able to use all 999 memory slots for RX/TX whatever I want, as long as they are within the FRS/GMRS frequency band. I imagine the KG-905G (less expensive option) will allow the same.
If you want simpler/cheaper, I think Baofeng UV-9G will allow full use of all slots, but I am not 100% on that.