Sid's mask is a gas mask and he has around 8 of them. So there are no real instructions for his mask, simply go down to your local army store and pick one up at a cost of around $8 / £12.
The white mask is called "Schutzmaske SchMs", it is supposed to be quite common. A black version of this can be bought @   Respir . The best place for the white version is auction sites such as Yahoo Auction or Ebay NOTES: The Schutzmaske SchMs was designed for optical device usage and came equipped with a highly effective speech diaphragm

One of his other gas masks can be bought here: Maine Military Another of his masks can be bought here: Major Surplus Survival This is the Swedish gas mask.

IOWA Mask (a): Buy a British Civillian Duty Respirator or a Canadian M-69. (very similar to the Duty Respirator). You can buy the Canadian M-69 at http://www.majorsurplusnsurvival.com . Once you get either mask, take all of the filters out and then you will need white or black clay for the teath. It doesnt matter which cause one of Sid's has black and one has white. Look at the picture of Sid's new mask at the cover of the latest issue of REVOLVER or on this website. Once the teeth are done, there is still more things to do. You will need a bondage hood. you can either put the gas mask on over the bondage hood or you could hot glue it together.  You will need to cut out ear holes. Once that is done, you are almost finished. If you want to add further details, look at his mask and get some black clay... On the eyes and all over the hood/mask you can sculp and mold on detail to make it look more like a skull. There you have it!!! I pretty decent Sid mask. If you want a better effect, paint your face all black or a comination of red and white. That is what Sid does. Sid also has a black version of this mask so if you want that one, i would suggest to paint the mask/hood white unless you can find a white gas mask that can be transformed to look like his new one.