Custom-made mask. The concept seems to be that the mask was made out of a human skull and horse teeth, with metal accents. Two hoses run from the mask into an bladder on his upper back.
The armor also looks like custom-made vacuum-formed clear plastic. The armor has tan edge trim (possibly self-adhesive moleskin), and is decorated with bottle caps, modified medals, and cell phone parts. One fan believes the PC board could be from a Nokia 3100.
Tiny piston. Piston from piston key chain. Can be found on eBay.
Dark brown leather codpiece decorated with castle nuts.
Boots and Shin Guards
Lace-up boots with piston heads as toe caps. Brown leather (belly leather is best) shin guards with lots of emblems on them.
If you can 3D print, here are the emblems: http://www.thingiverse.com/thing:978497
Colt Anaconda, 44 magnum (Python is similar and maybe easier to find airsoft versions)
During the ceremony which rains water upon the general public, Joe wears a dark brown kidney belt with the Immortan Joe emblem (made out of a motorcycle gear) on his belt.