The least expensive method to rust a sheet of metal would be a light spray of salt water. Even ordinary water will rust steel if it's not particularly rust resistant. I've used 4130 chromoly steel which rusts overnight if left with moisture on the surface.
Diluted chlorine bleach will cause rapid corrosion in aluminum, nearly instantaneous, but I'm not sure if the same effect will happen with steel. Chlorine is corrosive to steel, it's the time involved that I'm unsure.
The corrugated certainly looks like galvanized steel where some galvanized has corroded. You need to remove the remaining zinc . Dissolving it with hydrochloridic / muriatic acid would be fast , 10% should be strong enough.Salt water, vinegar, citric acid etc, would do it but slower. Once the zinc is gone it should rust pretty fast , a little dilute salt or acidic water spray will speed it up.
A mixture of hydrogen peroxide, vinegar, and salt will cause steel to rust at a fast pace. Usually within minutes. I've put to mixture into spray bottles and it has given rusty results.
16oz Hydrogen Peroxide 2oz White Vinegar 1/2 tbsp of salt