I recently published a new replacement part on Thingiverse. I recently found the shattered remains of the push button of one of my X10 wall switches sitting on the floor. I picked up the pieces, mocked it up in OpenScad and printed it out on my Thing-O-Matic. Works like a charm. Now I just need to order some white plastic. The model can be found on Thingiverse here:
X-10 wall switch replacement button