What do Floquil Grime and Foundation correspond to in the Polyscale line?
They don't. Grime was one of the pre-thinned weathering colors and Foundation was meant as a bare wood color for accepting their line of wood stains.
Grime was lighter than Floquil grimy black, probably not that much lighter than Pollyscale Grimy Black (which is lighter than the Floquil version) But a little white or light gray should get you close.
Foundation might be a lightened shade of Aged Concrete... or maybe a one to one mix of CSX Beige with Old Concrete...