Fuel Injector Seal missing

I started to do a LIM gasket job on a 2002 Buick Rendezvous with a 3.4. After taking everything apart, and placing the new gaskets in, I went to prep the LIM and fuel rail. I did take the fuel rail off to get to a bolt. Three of the injectors stayed in the manifold, and three are on the fuel rail. The problem is, one injector that is not in the manifold is missing a rubber seal that holds it into the manifold. Not the o-ring. This looks like a black molded plastic piece that was pressed onto the manifold. Any idea on where I can get this part? Autozone has never seen this before!

Thank You!

The black plastic cap on the end of the injector is not serviceable as far as I know. You can either reinstall the old injector without it or replace the injector.