Two episodes of the Japanese dub have been found, The Polka Dot Umbrella and Leaky Faucet, which is in three parts. Even though the episodes are the English and Japanese audio combined, it is not a voice-over, because if you switch to the left audio track, it's an actual dub. Gilby1385 has found an image consisting of eight Japanese Oswald DVDs. Now let's hope someone can buy those DVDs and rip the Japanese dub for YouTube.
Two episodes of the Japanese Oswald were found.