I've discovered D&D Miniatures are well suited to Ry20. The vast majority are CR <7*, and of those that are above CR 6, a fair amount are monsters that can still be used in a way. In fact, it's quite fun to look through my above-sixes and work out where each one belongs in a Ry20 campaign:
the CR 11 Stone Golem that guards the entrance to an ancient kingdom...
the CR 8 Warforged Titan whose creation ended a border dispute between two nations...
the CR 9 Aspect of Orcus isn't an Aspect, it's the Orcus...
the CR 8 Efreeti you hope stays in its lamp - because if it broke free, it could raze cities...
the CR 7 Yuan-ti Abomination which heads the empire-spanning Slithering Cult...
the CR 7 Bulette that destroys every caravan to venture through the Wastes...
the CR 13 Huge Red Dragon that is the first dragon, the dragon from which all others sprung...
the CR 8 Treant which is the heart of the deepest forest in the land...
*From the ones I've got. I've not bought them in a while, so I'm not sure how they've changed.