I have not unless it's a fantasy piece or a test/trial strike intended for approval for the 1965 coins.
The US mint did make 1964 dated silver quarters in 1965 and early 1966 so I wonder if any clad blanks made it into the 1964 quarter stamping area by mistake.
There is a single known 1964 (P) clad quarter. It's a fairly nice specimen and in high grade AU. The strike is a little weak but the dies were good.
Yes some are know to exists. Also several Special Mint Set 1964 are know and that is what your posted quarter looks like, a SMS. It's a beauty.
