Minecraft – Are there places where pumpkins are likely to occur

The usual way to do this (for any mob) is put open trap doors in the pit. Mobs avoid falls now, but will treat trap doors as walkable blocks regardless of whether they're open or closed, wander over them, and fall.

The 5 I've found so far are these:

1: An item entity dropped near the Queen Ant. Not entirely sure if it was supposed to be like that or if that was a bug.

2: Inside the tree. Climb the jumping puzzle to the top and hit the button.

3: Inside the bed, in the house. Near the left leg at the foot of the bed is a set of stairs you can use to climb into the bed, which harbors "bedbug" spawners and cobwebs galore. Fortunately it gives you a sword at the entrance to this area.

4: Inside the bookcase, in the house. The forward-facing wall of the bookcase has a hole in it. Enter the hole, and complete the maze. Take the ladders up every time you find one.

5: Inside the pond. In the edge of the pond away from the house, underwater, there is a hole. Once you go through, the floor goes away, so hold space to keep your head pressed against the ceiling so you don't fall into the void. It looks like a dead end at first, but at the end go up, and you'll soon find yourself in a vast watery maze. There should be a quick path to the top where you will find a chest with a respiration III diamond helmet. Once you've grabbed that, make your way back down to the very bottom of the maze. On the floor is an area of glowstone. Break it and go down. In the chest is the pumpkin, and the button takes you back.

6:???