Walter Piston composed several concertos throughout his career, but there's no specific work titled "Piston Concerto for Flute and Orchestra" listed among his compositions. Perhaps you're thinking of a different piece or have confused it with another composer's work.
Walter Piston did compose a Flute Concerto, which was written for flute and string orchestra in 1938. This concerto is considered one of Piston's notable compositions and is performed by flutists worldwide.
If you have more information or a different work in mind, please let me know, and I'll provide any available details.