These are the part numbers for the reed valve assembly from page 19 of the X-Wedge parts manual. Maybe one of the custom bike manufacturers who used the engine would have one in stock? Just a thought.
6. Reed, breather valve, X-Wedge. . . . . . . . . . . . . . . . . . . . . . . . . 36-7031
7. Stop, breather reed valve, X-Wedge. . . . . . . . . . . . . . . . . . . . . 36-7032
8. Screw, BHS, 6-32 x 5/16", stainless steel . . . . . . . . . . . . . . . . 50-0060-S