There is no universal spellcasting focus magic item in D&D 5e.Instead, every spellcasting class has its own. They range from the warlock's Rod of the Pact Keeper in the 2014 Dungeon Master's Guide ...

Finding Humanity Alongside Druids, Demons, Tabaxi, and War Veterans ... pelt—of Raven Mist, a Tabaxi rogue. (In non-D&D terms, picture Indiana Jones with cat ears).