Welcome to the forum
While I cannot tell you how many special edition W72 Trans Ams were produced at the Van Nuys CA plant, I can let you know this info which is from Pontiac Motor Division. I also have this info listed on my W72 page which is on this site.
"Pontiac production records show 8,326 Trans Ams produced with the W72 Performance Package, 3,982 cars at the Norwood, OH assembly plant and 4,344 cars at the Van Nuys CA assembly plant."
"Pontiac production records also show 367 Formulas were produced in 1979 with the W72 Performance Package, 152 cars at Norwood, OH assembly plant and 215 cars at the Van Nuys, CA assembly plant".
To the very best of my knowledge these numbers are no where else to be found on the internet as I do not believe they have been made public up to this point.
I do know there is one other site with production numbers that is listing information from my W72 site on theirs.
Hope this helps.