Millenium FX used to make the clockwork mask, but they're no longer being made. You can do a decent approximation yourself by using the V for Vendetta mask as a base.
Here's mine that I recently completed without the porcelain crackle effect. I haven't decided if I'm going to crackle it with my current product (valspar porcelain crackle) because it seems to make the crackles too small.
I used vinyl spackle to cover the moustache/raised edges of the V mask. Flexible and sandable, but I couldn't get it perfectly smooth.