I am trying to find d&d dice sets marked with Japanese characters. I've only been able to find d10 sets. Is there any place I can buy complete sets (d4, d6, d8, d10, d12, d20)?
The following sites do custom dice, so you can send them your kanji et voila.
Koplow Games makes d10s, as you've noted. They also make d6s, numbered from 1-6 or 7-12. (You can find them on pages 70 and 71 of the linked catalog. The d10s are on page 75.) Your local game store should be able to order them. There are no d4s, d8s, d12s or d20s.