I found some near the lot by the top of the waterfall in the Bramblewood neighborhood. Near that liveable/buildable lot there’s a path that leads to a bench and there are some mushrooms growing near that bench. This is not the bench the Creature Keeper sits at, which where I thought I was at first until I looked around a bit and realized where I was. I also found some along the river bank in the Bramblewood, I believe near the fishing spot there. They’re hard to spot especially if you have Seasons and they’re not in season yet. So I recommend hovering over very bare dirt patch because that’s how I found my first set. For the spicy mushrooms you can also buy those at the stalls to complete the errands or plant them or both. But the other varieties can only b found by foraging from my understanding so if you can find them and harvest them I recommend planting them on your lot too.