There has yet to be comprehensive recordings of the orchestral and chamber music of the phenomenally talented Gavriil Popov. His First Symphony has been the most often recorded, perhaps due to its influence upon Shostakovich's Fourth Symphony. But most of his music, and he composed quite a bit of it, remains unrecorded. Ditto the works of Japanese composers Moroi Saburō and Kishi Kōichi. The former's Third Symphony was probably the finest classical work to come from an Axis country during the Second World War;the latter was regarded as being something of Japan's great white hope in the 1930s. Kishi was a gifted composer and, according to reports, conductor. I believe he was the first Asian to conduct the Berlin Philharmonic Orchestra. Unfortunately, he died at the age of 28 from a heart attack that resulted from peritonitis.
Over in Latin America there are tons of worthy composers whose work has been neglected on records, despite their importance in the development of classical music in their home countries and the region at large. One of these is the Chilean composer Domingo Santa Cruz Wilson, whose work was admired by Copland, earned a couple of mentions in Eric Salzman's Music in the Twentieth Century: An Introduction. Nevertheless, his music has not been recorded much at all. Even in Chile, where his work is considered important in the curriculum of the music schools there.
One more unjustly neglected composer on records: the Bulgarian Lyubomir Pipkov. The first time I ever heard of the name was way back in high school, during the initial stages of my Shostakovich obsession. I came across (maybe in the Boris Schwartz book on Soviet Music) a quote from an American interview Shostakovich gave in 1973, wherein he held up the work of Pipkov, along with Prokofiev and Britten, as being among the most interesting of recent years. Aside from a couple of vocal works and his Clarinet Concerto, nothing of Pipkov's has appeared on CD. If one digs around in LPs, there are a few more things available, but not much: his First Symphony, final two string quartets, and his anti-war Oratorio for Our Times. The latter work ranks very favorably with, say, Britten's War Requiem or Tippett's A Child of Our Time; in fact, I may prefer the Pipkov work over those ones.
Would be great if Naxos, CPO, or a similar label could ever get around to filling these recorded repertoire gaps.