Circles and Blue Lug ship to the US super, super fast. As I mentioned recently on iBOB, I typically receive packages from BL and Circles in fewer days than I do from Rivendell.
Sim Works is the in-house brand of Circles, they have stuff custom run mostly by other manufacturers, many in Japan. They have a US office in Portland, Oregon located inside the Chris King manufacturing warehouse.
It makes sense to me that these super shops in Japan have an easier time stocking Nitto products, especially the odd and esoteric ones. There are certain stems, racks and other bits I haven't seen at any US bike shops.
If you're ever looking for Nitto parts it's always a good idea to check BL and Circles. There might be other good shops, too, I just don't know of them... yet!