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).
It is (proto-)Theodotion’s reading that Paul reflects in 1 Cor 15:54. On this passage, see also the recent survey by John Meade.