In Saving and Loading Your Game ( https://docs.unrealengine.com/en-US/Gameplay/SaveGame/index.html ) the documentation recommends you to use Async Save Game to Slot for saving your game data, but no node with that name can be found from the search with or without context sensitive search option. Only non-async Save Game to Slot can be found. Same is true for load game nodes
I just tested and the nodes are in .24 and earlier when it was added and they show up in the Game Instance and Game Mode.
I have a feeling the problem you are running into is you are trying to use the node inside a function where it will not work. As this is an async node, it does not execute immediately and return immediately when it is done, it cannot be put anywhere but inside the main event graph. This is similar to a Timeline or a Delay node. Try to find these nodes in your main event graph and they will show up, try to find them inside a function in that graph and they will not show up.
