Yeah new symphonies don't get performed much in the public. New music still is a bit of a taboo in the classical music world, which is a damned shame, for it shouldn't be. It wasn't 100 years ago and it should not be today. It is the reason why the general classical music crowd doesn't know anything about new classical music.
That said, you can find almost anything at Amazon. The three names I mentioned are a great starting point. For some more great symphonists of today, take a look at these: Valentin Silvestrov, Per Nørgård, Witold Lutosławski, Carl Vine, Alfred Schnittke, and there are undoubtedly many others. Just spend some time on Wikipedia and you will come up with more names.