Amazon.com: DTECH 4K HDMI Dummy Plug Display Emulator Headless Ghost Adapter Compatible with Windows Mac OSX Linux Support 4kx2k 2160P 1080p for Computer Desktop (fit-Headless, 5 Pack) : Electronics
Amazon.com: HDMI Dummy Plug Display Emulator for Headless PC 4096x2160@60Hz, 3 Pack 4K Virtual Screen : Electronics
HDMI Dummy Plug : ID 4247 : $3.50 : Adafruit Industries, Unique & fun DIY electronics and kits