Isn't there a Japanese company making shutters?

Aggie different size lenses need different size shutters. Basically bigger and faster lenses need bigger shutters. Some companies [Fuji anybody else?] seem interested in keeping the shutters they use small.

A bigger shutter is heavier and they have less speeds. A 0 will top out at 1/500 I think. A 1 at 1/400. It's gets slower.

You basically are stuck with whatever the lens you want needs.