This page, part of Roger Pearse’s Tertullian.org site, lists Brepols’ venerable Patrologia Orientalis series by volume, including the contents of each, which usually include diverse texts in more than one language (Arabic, Armenian, Coptic, Ge’ez, Georgian, Old Slavonic, and Syriac). When a volume exists on Google Books or the Internet Archive, a link is provided; the last available book is volume 25 (1946).  Though not all of the series is available (in contrast to the Patrologia Graeca and the Patrologia Latina), this is still a very useful reference.

http://www.tertullian.org/fathers/patrologia_orientalis_toc.htm