My Re-Tail sucks. It rarely updates.
mine never used to update until i, er, "encouraged" my villagers to buy things by pushing them until that "ping!"-sound appeared. then i talk them into stuff they actually don't really need but i want gone because i don't need them either. new items now appear one or two days after the old one was sold.
i don't know if that actually helps you but it works for me.

anyway, to answer the question - i'd agree with others that it would probably be the korean dlcs who are the rarest, followed closely by the japanese ones.