Dorman 611-176 (requires 2 boxes of 10) - Black Acorn Style Lug Nuts
I am using these with my black wheels. You could just go to any parts store and try to find some.....our size is 12mm - 1.5 IIRC (don't quote me on that). I can give you specifics on thread depth, cap length, cut angle, etc..... but I'm away from the store right now.
HTHs
Hood
Just searched the dorman site and found M12-15 Hex size: 19mm but they don't have any black listed that I can see.
Those should work. I'm just wondering if switching to an acorn style nut from an open ended style nut might be an issue. I'm going to check the local parts store before I order something online.