Best advice is to search for who bought most of the breeding stock from Claude McCallisters stock. His birds generally bred true blacks but breeding pure blacks is very difficult. Perhaps you can inquire on the Araucana club site.
I have a black tailess pullet 15 months old. Egg color is good. Have a blue that is her sister also. Also have a blue brassy back split for silver that is from hinkly and has tail. He is unrelated to the pullets. Not black I know but compatible mating and would produce blacks from the black pullet. Want to sell out of all of the auraucana's I have. Too many birds. Might have a picture of her.