What to ask for when they say you can't do that
Autocryl was a single stage intermix paint. As such, any toner could be technically used alone just like a mixed color. But some of the toners may not cover or hold out well by themselves. Black is an exception.
So now, if you approach a paint counter with this request and are told that the mixing toners cannot be used without other clear ingredients such as binder added...
Ask for any solid black paint code, to be mixed substituting the main black toner for any other color toner which is called for in that formula. This applies to basecoat or single stage mixes and assures proper product performance while keeping the color as black as it can be.