Yeah, I've been looking at indices published through various libraries and overviews that Google Books has on preview; I'm just not finding anything. 90% of 'em are with White detectives in America, England, or Commonwealth countries, and the ones set elsewhere are White detectives going elsewhere and being colonial.

I think at this point my best chance may be to look for stories that *aren't* in English-language Mystery canon : things that are too new/indy/obscure, things that are slipstream enough to have been filed under a different genre, or stories that came out of non-English-language writing communities that, if they do have English translation, are ending up among foreign-language books rather than mysteries. (Fr. ex, almost none of the mystery-genre sources I've found even mention Akechi, who's a classic Holmes pastiche and the opposite of obscure - but apparently only if you're Japanese or an anime fan.)