I notice there's a tile in the in game wiki, "Vesta gaseous solution methane (tile)" but I cannot for the life of me find it on the map. I've scanned a massive distance out using the "infiniradar" mod, but I still see none of it. This makes the "Algea methane treatment" recipe and its downstream products inaccessible.

I had the same issue. The formula that generates methane clouds might have similar output to the one generating sulfuric clouds and the latter could have priority. I had to change default generation params and regenerate chunks to find any methane source.