I am not sure this is the exact texture you need as not sure about holes distance and diameter. Anyway, it's possible to adjust them. After looking on some reference pictures I guess it can be something like this:
File comment: Scale 1/1
corten_metal_perforated_test_scale_1.png [ 393.17 KiB | Viewed 3310 times ]
File comment: Scale 0.5/0.5
corten_metal_perforated_test_scale_0.5.png [ 357.09 KiB | Viewed 3310 times ]
Perforations are not procedural — they are made with the blend map. You can play with the size by playing with UV scale of the blend map.
In case you have some textures, which you think the resulting material can be made of, post the link Google Docs link