Here are a few grayish-purple or dark purple acrylic colors that I found, that seem to work for the color in the picture.

Liquitex Basics Purple Gray

Liquitex Basics Dioxazine Purple (and a smaller option from Amazon of the same color)

Plaid - FolkArt Purple

Grumbacher - Academy Dioxazine Purple

Liquitex Soft Body Acrylic Dioxazine Purple