To provide a bit of closure for those who find themselves in a similar situation, ChipQuik makes GC10 under their own name. It is their “thermally stable solder paste NC (no-clean) Sn96.5/Ag3.0/Cu0.5 T4” stuff that is GC10 but under a different name. This is my first venture into solder paste so I don’t have anything to compare it to. However, it certainly seems to work just like how others have described GC10.