it might help to know what you are asking for is called a negative edge, or falling edge DFFR, active low set is called just a reset, DFFS and a DFFR and a DFFRS, set, reset, set or reset depending on which node is tied low. I havent come across many synchronous sets or resets, but you could easily turn any dffr into having a synchronous reset by adding a latch on the reset node. I believe I have used something like this a few years back but it was a handmade synchronous reset dffr using pass fets. I also agree with barry this should be in asic.