Revell has a paint color cross reference chart https://content.revell.de/downloads/usa/TES_Revell_Paint_Match_Guide.pdf . The replacement paint for Revell Anthracite is ModelMaster Schwarzgrau RLM66. I would guess that the ModelMaster paint is no longer available. Revell also references a Poly Scale paint (Flat Black), but that paint no longer exists. It's too bad that the chart only references Testors paints.
You mention that the real Blackbird paint had blue in it. I wonder if Tamyia gunmetal blue paint followed with clear flat would work?