During the Halloween Event going on in Guild Wars 2 players will be able to carve Pumpkins for their chance at the Pumpkin Carver achievement. In order to get this achievement you will need to carve a total of 150 pumpkins which actually doesn't take too long if you do it right. The pumpkins reset daily or each time you enter an "overflow server" unless otherwise patched when you're reading this due to explotation of this very method.
The most common place players go to farm up these pumpkins is in Lion's Arch (LA). There are about 10 - 15 easy pumpkins to get to in Lion's Arch, the other pumpkins in Lion's Arch are extremely annoying to get to (like in a jumping puzzle, who feels like doing that? Not me!) Below is a map I put together of all the pumpkin locations I know of. As always you will need to click on the map in order to enlarge it so you can view it. The pumpkin's locations are marked with a little blue dot on the map.
Important Note: Use the Overflow Servers to your advantage when Pumpkin Hunting. You will be able to carve Pumpkins not only in the Overflow servers but also on your primary server. All three of the locations listed on this page commonly have Overflow Servers during this event.
Aside from Lion's Arch there are a few other places you can go to carve some pumpkins, I am going to go into these locations below this paragraph.
Queensdale Easy to reach Pumpkins
Queensdale has a bunch of easy Pumpkins to get too, there are about 10 I didn't put on my map since they're quite a run away from the "main pack" just south of Divinity's Reach. But chances are if you do Mad King's Labyrinth (about 20 in here), Lion's Arch (About 10 here) and Queensdale (about another 10) every day and also keep using the Overflows to your advantage you won't have to worry about going out of your way for annoyingly frustrating Pumpkins to get.
As always click on the picture below to enlarge it.