You need to find a Desert Wetlands sub-biome, which you can easily tell apart by the presence of quicksand. It has a 33% chance of spawning, and since every desert planet can have multiple sub-biomes in it, the final spawn chance will be even higher. The sandspitters won't appear in every instance of the biome, but they will be found in the majority of them.

If you are using Frackin' Universe as well, the sub-biome spawn chances decrease drastically. FU adds a lot of new sub-biomes to the spawn pool, so your chances of finding specific sub-biomes decreases quite significantly. It's an unfortunate side effect of the additional world variety added by FU.

Well ♥♥♥♥. I had the idea that FU could be the issue. Thanks anyways. Would be nice to find another sources like sandspitter farmers or something like that.