Try this link over to gleemax.
In his trade list he has “orphans,” that is, cards w/o pieces. You might be able to work something out for at least some of your pieces.
I have seen them on ebay in the last few days. Search for “axis and allies japan” to narrow the search to about 20, then look at the seller’s other items to find the rest of what you want. Otherwise you’ll wade through about 1500 to 2000 items. “Revised” may just bring up the entire game.
I dislike playing the US the most. They are far from the action and are powerful. By the time they seriously get involved in the fight, they rip through the lines of the Axis and then it’s about over….I enjoy the more challenging position of the Axis…