That part is still "being retooled" per Chip's website...this has been up since at least March of '07.
I bought a barely used SW1911 from a pal of mine which belonged to his deceased father. His dad had owned the gun since new and he hadn't shot more than 300 rounds through it,all at an indoor range,not ever holstered or dropped or put through any handling drills... it definitely fit the term "lightly used".
The CMC thumb safety is in horrible condition,the portion of the part that rides the plunger and the detent do not line up properly (apparently because of how it was designed) and the safety has a very loose,"uncertain" feel to it. Also the finish is worn and it looks like crap.
I learned of the retool situation when I went looking for a replacement.I'm very curious as to why it is being retooled and also why it is taking so long to do so,was it redesigned or did the mould wear out?
RickB has it right in my opinion,the CMC thumb safety is ugly

...but to address mes228's post,it seems this part is unavailable from the manufacturer at this time.