HollyWood Studios
I have only found Sheffy at two locations at Hollywood Studios but the last three times I have been there, it has been reduced to one location.
To find the Sheffy, make your way towards Galaxy's Edge. It is located on the left side of the park but you won't actually go nearly that far.
Before you get to Star Tours, the original Star Wars ride at the park, you will walk past the big Dinosaur in the lake, you will see Indiana Jones Stunt Spectacular to the left and you will see signs for the Olaf meet and greet to the right. Next to Olaf are the bathrooms.
In between it all, as you start to make the turn towards Star Tours, there is a little beer cart and that is the only spot you can get Sheffy at the moment but there has been some talk according to a cast member that they may add it to a cart on the other side of the park on the strip to Hollywood Tower of Terror so be on the lookout!
Animal Kingdom
There is an almost relief when you are walking through a park on a hot day and come across a refreshing sign that beer is available. At Animal Kingdom, you can find Sheffy in Pandora!
As you enter Pandora from the main entrance and not from the back entrance from Africa, you will find a beer cart next to the rocks where you can bang on the drums...across from the bathrooms. If you are standing in front of the Na'Avi River Journey entrance, you have gone too far.
So far, this is the only spot I have found at AK that sells it.