Perhaps, many distributors are not carrying anything made from Diamond because certain brands of their dog food have contained a contaminated toxin that lead to many deaths. Dogs in 22 states have died as a result of ingesting this brand's product that has been contaminated with Afatoxin.
Even though Chicken Soup was not on the list of brands that contained the grain contaminated with Afatoxin, (CS doesn't contain corn) many people still believe the company is irresponsible. This could account for some distributors not carrying it anymore. I'm quite sure the company is still making it though.
You can google Diamond Dog foods for more information. This link carries good information.
http://www.snopes.com/critters/crusader/diamond.asp
Nancy