I mean, I do have some coworkers and friends who speak Japanese, so while I wouldn’t have dozens to choose from, I think I’d still be fine.
And it’s not quite the same. English is spoken a lot more than Japanese. None of your Japanese coworkers speak English? Obviously you don’t actually need dozens of affadavits. A few should suffice.
Also, it was not clear to me until after my post that the proof needed to not be in Japanese. But that goes beyond sworn statements, right? Presumably most proof that you lived in Japan would be in Japanese?
Anyway: sorry my suggestion wasn’t more helpful, but I’m glad you have things figured out.