The Vatican Library has made available a digital facsimile of Codex Marchalianus (7th–8th c.). The codex contains some prefatory material and the text of the prophets, including Baruch and the Letter of Jeremiah. Each page has two scans with alternate lighting. Below is a sample of the marginalia from Isa 25:8 (leaf 231) that notes the alternate readings for the passage in Theodotion (top) and Aquila (bottom).
Since 1875, Frederick Field’s edition of Origen’s Hexapla has been the standard reference for the work. A new edition is in preparation under the auspices of the Hexapla Project. But, for the present, Field’s work remains an invaluable resource. His two-volume edition is available via Internet Archive.