Records International (USA) are a good source for some of those hard to get composers. I have dealt with them for years, and his service is excellent, usually within a week to Australia. I do not think he carries big quantities of initial stock, so it is best to check his monthly catalogue on the 1st of each month, but I have had instances of ordering, and the item was out of stock, or didn't arrive, and months later he would email me to ask if I still wanted the item. But if you order early in the month there is usually no problem. The manager is Jeff Joneikis, and all of my emails to him are always promptly answered.
I deal mainly with MDT, Presto, Records International, JPC, Arkiv. But because Australia is so isolated, I have dealt directly with companies in Poland,Czechoslovakia, Sweden, Denmark, France, Italy, New Zealand, Portugal, Spain, particularly when I see something in their catalogues. For instance, I recieved the symphony of Vianna da Motta, Piano Sonatas & Symphonies of Bomtempo, & Symphonies, Violin Concerto, Tone Poems of Freitas Branco, from Portugalsom, because I was having trouble getting them elsewhere at the time. As far as I know the da Motta symphony has not been realeased elsewhere ? To access these different retailers, I searched google "CD retailers worldwide"
Marcus..