The large single piece "turtle" cover you'll find on ebay.com.au fairly easily.
I do not know if this will have fitting issues.
Freight to USA would be a nightmare.
The 2 piece covers are very similar to 2004 GTO engine covers.
Left is 92067293 and are available
Right is 92067294 and Holden have no stock (could be waiting months).
These have text "5.7 Alloy V8" embossed on them.
These clip over the fuel rail in 2 places each and sit onto 2 pins each which thread into the rocker covers.