The underprinting is done by Giesecke & Devrient in Munich, currently RBZ is paying €500000 a week for paper from them, then the final printing is done in Harare. With this arrangement one ponders given the rather simplistic design that counterfeiting could be a problem. But with the largest denomination only worth an also sinking US$2 perhaps it is not worth their effort.
Pretty soon I think the US will be doing the same thing, creating more inflation to wipe out all it's debts so it's government will finally be solvent after 10 years of huge budget deficits.