Hunh. I've been working with gas monitoring for years (mostly during my volcanology PhD) and written lots of code to interface with many CO2 sensors, usually as part of packages that talked to many other sensors. Other than some weird binary protocols, it was all straightforward, brainless code so I never thought it needed to be published. LMK if anybody wants a hand with anything specific.
I've used a few multigas sensors that had O2 when mapping volcanic caves -- Draeger Multiwarn, MultiRAE, National... Safety (?), and CrowCon GasMan. The CrowCon was my favorite by far. Disclosure: they gave us equipment for free as sponsorship for our expedition, but it was also honestly just way better than the Draeger or RAE. Great datalogger built-in with good serial interface, small, waterproof enough for our uses (the others said IP68 and still died of water damage). I suspect all CrowCon products are quite good and cheaper than the competition.
Or, if you're building your own unit, then I remember citytech (welcome to city tech!) was pretty much the only option when I was doing it. The circuits to run electrochemical gas sensors are a little annoying to set up.
