I thought I'd just note down some of the things I do when looking to see if there's a Japanese translation. I'm not a bibliographer by profession. So it's a fairly amateur search and I'd welcome any better suggestions.
Sites on Japanese works translated into other languages
(I found the first two of the websites listed below from the sidebar of the blog Contemporary Japanese Literature, the third from the sidebar of the blog Ho-Ling no Jikenbo.)
1) Perhaps the most useful site is the Japan Foundation's database of translated works. I've always gone to the author lists, which are alphabetised by surname. Within the results, to find out what exactly each entry is, you need to click on "Detailed display".
2) A site I rarely look at is Japanese Literature in English. My impression is that this is very incomplete. On the other hand, I have found things there that are not listed on the Japan Foundation's site.
3) For mystery, instead of a database, there's also a website, Asia Mystery League, in Japanese with lists for various European languages. Of course, if you want to read a translation from Japanese, it's quite likely that you don't read Japanese; but as most of the relevant pages have lists including the Romanised form of the author name, perhaps it could still be of some use. The European languages are all on separate pages: English; French; German (no European alphabet form for the authors, so you may find it not that helpful); Dutch (no European alphabet form for the authors); Italian; Spanish and Portuguese; Scandinavian and Baltic (no European alphabet form).
The sites above don't find everything. I often look on google and google books and in combined library catalogues like Worldcat or the Karlsruhe Virtueller Katalog. Worldcat allows you to select within the results by language. The different possibilities for spelling and ordering Japanese names in English can be a problem for this kind of search.
It might be interesting to compare the results of the different sources for a few authors, restricting the search to English translations.
For MIYABE Miyuki, a google search would return too much (since she's a well known author in the west). The Japan Foundation, Japanese Literature in English and Asia Mystery League turn up almost the same list of books and short stories: Crossfire; The Sleeping Dragon; All She Was Worth; Brave Story; Ico, Castle in the Mist; Shadow Family; The Devil's Whisper; "The Futon Room" in Tales of Old Edo (Kaiki: Uncanny Tales from Japan Vol.1). But Japanese Literature in English has one more: The Book of Heroes (2010). The Asia Mystery League has that too and does one better, adding, Apparitions: Ghosts of Old Edo (2013). As to catalogue searches, Worldcat finds all of these; but, combining as it does the data of many libraries, it also has some false entries (nothing to compare with Google Books of course). For instance, it offers a book Who's That Boy? from 1998; but the ISBN for that gives a book by Miyabe in Japanese from the same year, 地下街の雨.
For NIKI Etsuko, The Japan Foundation gives a translation of 遠い絵図, "The distant drawing" in The Kyoto collection: stories from the Japanese (Osaka, 1989). None of the other sources find even that.
For NISHIMURA Kyoutarou, The Japan Foundation finds a short story "The Kind Blackmailer" in Ellery Queen's Japanese golden dozen : the detective story world in Japan (1978) and a novel, The mystery train disappears (1990). Asia Mystery League has the novel but only lists the short story separately (not in its Nishimura entry); on the other hand, it adds the more recent collection, The Isle of South Kamui and Other Stories (2013). Japanese Literature in English doesn't have anything. Worldcat finds everything and adds a few irrelevant search results.