While I don't have the NBA rule book handy, the HS & college rule is that a "flop" is an unsporting act which is a technical foul - not a "no-call".
It's never called because you have to be damn sure before you give a tech for flopping and at full speed it can be awfully hard to be sure.
IMHO, it would be better to encourage more charging calls when the defender is still on their feet. It's never seen in the NBA because by that point players are totally focused on falling backward at the slightest contact. If at lower levels you called charges on little gaurds that launch themselves at uncorrdinated bigs that don't know enough to fall, then it would clean itself up naturally.
I call 'em that way at lower levels and get coaches beside themselves in anger because "how is it a charge if the defender is still standing!!!" That's what players are being taught by parent/coaches because that is what is being rewarded. Remove the reward for the behavoir and no punishment will be necessary.