I just spent my whole day--a real-life day, not in-game day--searching and searching for borax and limestone, to no avail. Tens of thousands of blocks traveled, far far from home. Exploring is my favorite thing to do in games, but even I have my limits. I got so exhausted I had to stop. I didn't want to use commands in this game, but with the ridiculous distance away from home I've ended up traveling on this fruitless search, I'll have to tp myself back if I don't want to spend a whole season doing nothing other than running over terrain.
Weirdly enough, I haven't seen a single mushroom on this whole playthrough, either. Wonder what's up with that.