Simplest form of RKCB - asking for kings after asking for queen
You should use specific king asks instead of count asks. In this auction, opener's 5NT denies any side suit kings; Eddie Kantar in Roman Keycard Blackwood suggests that it show a side queen, singleton, or doubleton, with a jump to 6S denying even that much. Kantar then suggests that a cue bid by responder is a grand slam try, looking for a third-round control in the suit bid.

1S-4NT-5D-5H-6C would then show the spade queen and the club King.

1S-4NT-5D-5NT asks for a specific King, promising all key cards; opener bids their cheapest K.

Obviously, this requires some discussion with partner, but not much more than "Q ask with specific Kings, 5NT specific K ask"; third-round asks and distinguishing 5NT/6S responses to the Q ask should not be used outside an established partnership.