In case you wanna do it yourself, here's the rules:

Each map entrance has 4 pumpkins
Pumpkins are not inside the actual tombs, but the areas outside
You have to get all 40 to get the cosmetic

Cursed Sand Ruins

One On top of a collapsed Pillar to the right of the stairs
One Behind a rock on the left of the stairs
One behind the tent to its right
One next to the buried statue on the left of the tent.

Temple of the Pharaoh

One Buried in the Sand by the excavation site (near the car)
One Behind the statue at the very end of the Temple (Resting behind the pedestal)
From the entrance to the temple take an immediate left and follow the long outside hallway. The pumpkin should be at the end once you have to make a right.
From the entrance once more, this time take a right and follow the hall all the way to the end, then take a left and you should see the pumpkin once more

Crypt of the Great Pyramid

Directly in front of the spotlight, sitting atop some stairs.
To the left of the entrance behind a rock
Before you enter the area with your gear, take a left. It's wedged in some sand.
Behind the goat statue to the right of the stairs

Undercroft of Akar

Inside the Excavation site
Behind the barrel of Oranges
By the entrance to the tomb, near the statue on the left
Behind the large square stones near the tall wall of sand to the right

Sunken Dune Shrine

Inside the Excavation Site
By the spotlight overlook the Excavation Site
Atop a circular stone to the left of the tomb entrance
Underneath the Laptop.

Hidden City in the Sahara

To the left of the jeep, in an alleyway between the two houses
Under the Balcony to the house in front of the cloth market, wedged in between the wall in the pillar at the far end of the map.
In front of a door directly above the Tomb
Inside the Entrance to the Tomb, between the two statues immediatly to the left

Sobek Oasis (Night)

Underneath some stone, near the truck end of the river, on the tombs side
Behind the Tent
Nestled in a Bush on the tomb side of the river, near the waterfall end
Underneath the Waterfall (in the water)

Sobek Oasis (Day)

In the center of the river, closer to the waterfall
In a patch of bushes, closer to the waterfall, on the car side of the river
At the end of the river, underwater, between the two rocks.
In a patch of bushes near the car.

Dread valley

To the right of the stairs right by the car
At the top of the road, once it evens out, take a left and head through the sand to a tall stone wall, the pumpkin is on the right of the stone wall.
Behind the leftmost pillar of the two pillars at the end of the road
Inside the tomb, don't turn right to go to your gear, instead go behind the barrel, the pumpkin is next to a pillar.

Nekhbet Chasm

By the man with the radio. Head towards the rocks by his tent, run at various angles until you get up. It's right by the car, you should see it when you sapwn.
Near the end of the road, behind a large stone atop some wood planks.
By the second platform on the opposite side of the road, on the clifface
Under the stairs, near the bottom, among some pots.