In good working condition Tektronix  elastomer key mat removed from TDS744A. Part number: 214-4287-00

It used in all TDS5xx, TDS6xx, and TDS7xx series Tektronix oscilloscopes, including:

TDS510A, TDS520, TDS520A, TDS520B,TDS520C, TDS520D, TDS540, TDS540A, TDS540B, TDS540C, TDS540D, TDS544A,TDS620, TDS620A, TDS620B, TDS680B, TDS680C, TDS640, TDS640A, TDS640B, TDS644A,  TDS644B, TDS684A, TDS684B, TDS684C, TDS694C, TDS724C,TDS724D, TDS744, TDS744A, TDS754A, TDS754B, TDS754C, TDS754D, TDS784A, TDS784B, TDS784C, TDS784D, and TDS794D ( the list is not complete).

Contact me if you have any questions or not sure if it is compatible with your scope.