Adorama has the Fujifilm EVF-TL1 EVF Tilt Adapter for GFX 50S in stock. You can purchase it also at AmazonUS via Adorama.
Fujifilm GFX EVF-TL1 EVF Tilt Adapter: BHphoto, Adorama, AmazonUS
Fujifilm GFX: USA BHphoto, Adorama, AmazonUS EU: AmazonDE, CalumetDE AmazonUK, WexUK, ParkCamerasUK, PCHstore AUS: CameraPro