Hi! There's a factory object called "midi/out/cc" which sends CC data when a trigger is received. I have never tried to use MIDI internally, but you probably have to select an "internal bus". There's another object called "midi/out/cc thin" which may not require a trigger - haven't tried that as well. If that doesn't work you could use a "logic/change" object to generate a trigger each time the value changes.
Another option is to use the internal modulation path: patch your analog GPIO input to a "patch/modsource" (needs to be triggered) or "TSG/patch/modsource auto" (no trigger necessary) object and adjust the modulation amount in the menu opened by right-clicking where you also assign MIDI CCs. In my experience this can get glitchy sometimes.
The best way probably remains to connect your analog inputs to object inlets directly - this way you have a higher resolution than via MIDI. I think Axoloti uses 12bit conversion for analog GPIO (4096 values) whereas MIDI uses a 8bit resolution (128 values) which can result in some audible stepping.
If you need to add inlets to existing objects check out this thread. It may be a bit scary at first, but most of the time it works by just adding the inlet to the desired parameter.