"SteveB" toquerville@zionvistas writes:

I found a source for new free corrugated 22 ga bare steel panels 3' wide.
I'm going to use them for a shade. The guy said they were 602 or something
like that, meaning that the coating on them deteriorates quickly and
intentionally so that rust can form on the surface giving it the old barn
look. Is there any spray I can put on there to hasten the process? I can
get all I want and in lengths up to 16', and for a tip, the fork lift
operator loads them for me.

Craft stores (Michaels, etc.) sell patination chemicals. Typically
people put on a sealer, then base coat of metal paint, and then apply
the patina chemical.

One of the chemicals explicitly says "rust"

You can skip the first two steps. :-)
But if you want to to a large area, it might be too expensive. :-)