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