DSCH Publishers Moscow is currently the Russian agent for Shostakovich's works. Website (English)

However, several other publishers also represent his works. Sikorski has released miniature scores of his complete symphonies, string quartets, and preludes and fugues. Also, International Edition New York published his Piano Trio Op.67 in 1987 (back when all of his works were public domain in the US). Boosey & Hawkes also has a few works (such as a miniature score of his First Violin Concerto Op.77), but DSCH is the main source, especially since they are behind the New Complete Works urtext edition, which when complete will be 150 volumes strong.