I don't think Godot has an Asset Store/Marketplace like Unity and Unreal do. I do believe it has a store of sorts for extensions (correct me if I'm wrong). A good place to find game artwork is opengameart.org and itch.io. If you need scripts, what I did when I used Godot is browse YouTube tutorials, most of them have a link to the code used in the description, though some like to hide it behind a paywall.