You'll be lucky to find a modern presentation of a Clark Y. Most of them will show the position of the "center of pressure", which is an obsolete and useless quantity.
This chart for an NACA 2412 will show what modern data plots look like, with the data plotted at different Reynolds numbers.
The pitching moment is usually negative for airfoils of this basically generic shape.
The CY-H's reflex makes the Cm positive a bit.
It's not usually something to worry about with a model... just put some reflex in the trailing edge of a flying wing, and adjust to your needs as you fly it.
Andy Lennon's "R/c Model Aircraft Design" from MAN has more than sufficient data to design any r/c plane, with a good chapter on tailless. Martin Simon's "Model Aircraft Aerodynamics" has more theory, and is also something to put in your library.
This site says it has Clark-YH data..