Where are the Iron Golem spawn eggs?

Iron golems can not be spawned with spawn eggs like with other mobs. Like a snowman, you need to build a shape and then put a carved pumpkin on top. The shpe you need for iron golems is one iron block on the bottom, then three on top with the one on the bottom being in the center of the top three, then put the pumpkin in the middle of the three, and directly above the original block.

If you want more info, you can look at the creation section of the wiki.