I suspect it's closer to having any deal than being exclusive. For Grand Compe and Sun XCD, someone has to decide to buy them in Japan and bring them here. Both have home markets, so the trick is hunt them down in Japan or find an exporter.
People like Soma, VO, Compass don't carry the whole line - they go shopping in Japan and bring home what they believe they can sell.

I think the success Grand Bois and Alex Cycles has selling across the big pond, as long as the JY doesn't get too strong, we will see an improving mail-order market for Grand Bois and Sun XCD. Without the internet, the only source for any of it would be the Merry Sales paper catalog.

here, Universal Cycles imports a bit as well, also
https://www.universalcycles.com/search.php?q=dia+compe


And yes, SunTour indexing was a big fail, but it also took Shimano and Campy awhile to work out their bugs, too.