well, I think there are at least 4 ways to get real Japanese National shirt.
1. Have some insider that is a great friend with Japanese player. I actually got 1 shirt this way (Mizuno, now they are using Victas)
2. Be a part of the ITTF World Tour (volunteer, umpire etc). Got jacket from Mizutani (also Mizuno, that black one) after the tournament, but this is actually quite hard, cause they are not allowed to give away stuff. No idea why he agreed.
3. Japanese mercari, sometimes there are past national team members or friends of national players selling some stuff (rarely even that white packaged tenergy before dignics came out).
4. And the last one that is only theoretical, because no-one should even try it. I was at Stockholm Open and when the tournament has ended I have seen Mima Ito leaving the stage without her national jacket, when she was about to go out of the building she has noticed that something is missing and I have informed her that she has left it in the stand. Theoretically someone can wait and "hope" to take missing stuff...