ohh i've been waiting for this fish for a long long time.
unfortunately this fish is found only in japan, taiwan, thailand and surround locales.
as far as i know these fishes are not targeted for collection. occasionally some of them may get caught and end up being sold in local markets, some as food fish, some just as by catches.
it's not a fish that's not collected because it's rare or anything. it's just, for some reason that i'm unsure of, not being mass distributed to the world like other fishes.
the close relative, chaetodon auripes, is also not really encountered in the trade. but i've seen it in hong kong being sold for super cheap prices.
dr hiroyuki tanaka often encounter juvenile and small weibeli and auripes butterflies at miyazaki harbour, near the surface, where he lives.