Had a hell of a time finding any that weren't obscenely tight when I used to live in Japan a few years ago.
Fortunately, Okamoto started making bigger ones in the past few years, but they still aren't as big as the biggest American condoms.
They made one called "Super Big Boy" with a picture of a horse on the box that if I remember correctly was about the size of a Trojan Magnum, but last year we found the "Mega Big Boy" (with an elephant on the box!) that was about 7.5" long and 5.75" in circumfrence. I'm pretty sure that's their biggest condom period. Compare that to a Magnum XL and it's no contest, but then again, even in America, most men don't need an 8"+ condom.
All that said, I've got a Japanese friend with a 7.5"+ cock, so the stereotype about all of them being tiny simply isn't true. And I have American friends who buy Magnum XLs when they have sub-7" penises, which is both unnecessary and probably defeating the purpose. So part of it is cultural rather than related to the physical size in the country.
Like for the Korea example, consider that it's a very conservative country. It may be more that their society isn't open to the idea of horse-cock dudes swinging about (even if it's the reality for some of us) rather than that they have a significantly smaller average penis size.