Are you asking for actual chocolate or dun? I am pretty sure that all of the chocolate birds here in the US are actually dun. Dun works like the blue gene. I am pretty sure that chocolate is a recessive.
I know that the "chocolate" (dun) birds here in the US are polish, wyandotte, OEGB, fighting type games, seramas, there is rumor of dun sumatras, I know there is a line of white phoenix that carry dun so there are dun phoenix, I know there are some other breeders that are working on chocolate in other breeds. So far I think the chocolate orps are just in the UK and the chocolate silkies are in Holland as well as solid chocolate seramas. Then there are the other colors that have dun in them like dun laced, dun partridge, dun red, and other varieties.
I also love the chocolate runners, muscovies, calls, turkeys, and pigeons.