There are a couple European dealers I've heard of. Here is one a friend uses
https://minisatsuki.com/categorie-produit/satsuki/page/2/ I don't know if Kongo no Hikari is in their listing, but they do have some really nice stuff. Hino no Maru is all the rage
That was my satsuki btw. The thing is, it was actually showing all striped flowers. Kongo no Hikari does have red and white selfs, but they weren't showing in this early bloom. Consequently its unlikely that this plant will look exactly like this in the out years when the selfs start to show.... (However that's not going to slow me down from propagating cutting of it this year!)
The lesson I've learned the hard way over the past two years is not to fall in love with any specific color pattern, as those darn multicolored satsuki flowers will mutate in a heartbeat. Instead I suggest you concentrate on getting satsuki with characteristics that make them good for bonsai styling. These include: leaf and flower size, pliability and suitable hardiness for your climate.
Cheers
DSD sends