Bestbuy offers ASUS - ROG 65W Charger Dock - Supports HDMI 2.0 with USB Type-A and USB Type-C for ROG Ally - Black for $29.99 (orig. $64.99) free shipping.

Product Description:
Use the ROG 65W gaming charger dock to connect your additional accessories with the ROG Ally through one USB Type-C port. Support display output using HDMI 2.0 for your TV or monitor. Charge or connect through USB Type-A for your mouse, keyboard, or USB storage drive, all while charging your ROG Ally.