Great looking skid/underbody panel.
The "vents" are called loovers. Many hot rod/custom car builders will have a press than can punch out the loovers. Their width can vary according to punch size. Ask a hot rodder/custom car guy/gal if there is a body/custom paint shop nearby that does
LOOVERS.
Here is a 13 photo spread showing loovers, the die and press.
Hot Rod Louver Photo