Most Japanese artists have a Pixiv or Nijie account. You should be able to move most of your follows to those services.

A lot are also jumping ship to misskey.io, which you can follow if you use mastodon/pleroma/misskey/etc.

I suspect the small amount of holdouts will soon create an alternative as well.

Not exactly what you asked for but since you seem to care about it, you can use https://fba.ryona.agency/ to see what instances are blocked by what instances and vice versa. Here are the instances LW blocks for example.