The Xbox 360 gamepad is back, and you can pre-order it now - Polygon
Xbox 360 Wired Controller (Generic) - Game 4U
Amazon.com: Wireless Controller for Xbox 360, Etpark Xbox 360 Joystick Wireless Game Controller for Xbox 360 & Slim Console and PC Windows XP/7/8/10(Black) : Video Games
Xbox 360 wired and wireless controllers | Xbox Support
Xbox 360 Wireless Controller,Compatible for Xbox & Slim 360 PC Windows 7, 8, 10 – YCCTEAM
PSA: You can put xbox one thumbsticks on a xbox 360 controller : r/xbox
Side-by-side: Xbox One gamepad vs Xbox 360 gamepad | TechRadar
Wired Game Controller for Xbox 360 & PC (X-188) – DOYO Game
Xbox 360 Generic Wireless Controller - Game 4U
Xbox Accessories & Controllers | Xbox
Microsoft Xbox 360 Wireless Halo 3 Covenant Controller - Xbox 360 – J&L Video Games New York City