Don't bother with the factory plastic ones, get an aluminum one and it won't crack or break or leak like the plastic ones. I don't really think there are any original ones left anyhow.
I f you are going for a stock look, just paint it black.
TTA vacuum block has been discontinued by GM. I sent a friend to my source at a GM dealer who returned the news to me. Had hime buy the Kirbian's piece.