I just received my order of 12mm Araya spoke nipples today from the UK (via eBay).
As I had hoped they are the old JIS standard requiring a 3.5mm (3.45) wrench. (Park Red) 
I'm a happy camper as I still will have a source for my Japanese roadbike rebuilds. Here is a picture of my caliper measuring the wrenching size on the new nipple.