This year I purchased a "Russian" breeder queen. These bees are quite different in many respects from the assorted races of bees available in the US. They are a small, dark bee with many of the characteristics traditionally ascribed to the Caucasians in the previous posts.
They can produce large numbers of excellent queen cells and were amoung my best honey producers. They carry 1/50th the varroa mite load of my Italians and Carniolians and are unusually gentle and quiet on the combs.
I was concerned with their smaller cluster size going into winter but my recent inspection indicates that the bees are long lived and have survived the worst winter in the last 5 years(central Wyoming)in great shape.
This stock could be an excellent choice to try if you are looking for a dark bee in the US.