3rd party. my last batch $600 printheads are still going strong, now 3yrs later.
pretty safe to assume that they're all coming from the same facility, or at least the same country. it is just who orders what quantities, or wants to unload them quickly, or deserves a $500 markup for putting a pic of a man in a cowboy-hat next to it, is what determines the prices from resellers.
there is no such thing as a "mimaki" head. i once took apart a three head unit for an epson 10000 (has three dx4's). under the epson head rank sticker was a roland head rank, then under that was a mimaki head rank sticker. i've heard there's even a "head rank convertor program" that can interpret ranks from one OEM to another.