Often times the cover is actually part of the air bag assembly.
I agree with RightCoast, or you could check with a local collision repair facility.
Do not, and I mean do not, ever buy a used air bag....or let an insurance adjuster talk you into one. (This is just an FYI for all our viewers) If this would happen, contact me and I will guide you through the process to obtain a proper repair.
(GM certified collision shop manager, certified auto damage appraiser, and DuPont certified auto re-finisher)