Well, to add some creedence, Diamond distributing has been having issues importing japanese toys of late.
Same thing happened to Figma Samus and Link last year, for example. Knowing how Diamond works, tehy were likely trying/planning to import DIRECTLY from bandai, much like when they tried to import directly from Maxfactory.
Thing is, BLuefin already has the Tamashii imports exclusively for america. This means that Diamond would need to go through Bluefin... which would cost them more, and they likely don't want to do that.
Tell your comic shop guy to try contacting Bluefin directly about getting an account and ordering through them . that's what Derringer tells people to do on 4chan. I'm not sure how to go about doing that, but their website likely has the info.