SCA mins are 1/8" hole staggered at 3/16" spacing.
From that site, this will work but is not ideal:
http://www.onlinemetals.com/merchant.cfm?pid=13516&step=4&id=1004&top_cat=849
# 0.06" thick A36 Perforated Sheet Round Hole
(0.125" holes - 0.1875" stagger)
I've been using stainless for years, over 300 helms, and never had a face plate fail yet. I built one with mild and never used or sold it, as it was WAY to easy to form/deform. Its barely stronger than mask mesh.
Further, you're breathing through this and that's a LOT more surface area than a bar grill to grow rust... and more difficult to clean.
I'd recommend 16 ga stainless instead, part
http://www.onlinemetals.com/merchant.cfm?pid=13524&step=4&id=1002&top_cat=1 instead.
This stiff arrived half-hardened from teh punching action. Heat to red and allow to air cool to get a poor man's anneal before you start hammering, or work hot. You CAN weld this stuff, but practice on scraps as its melts like spider web under the flame or arc. I use a stainless wire in a 140amp mig, lowest setting, to weld this stuff to mild steel, although you CAN weld with mild wire too.
Edited to fix links