Player 1 and 2 buttons
https://www.amazon.com/gp/product/B01N5Y8E2Z/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Square buttons
https://www.amazon.com/gp/product/B06XBLH25X/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

These are powered from a USB cable sourced from a non-powered USB hub that I plugged into the USB out near the bottom of the monitor. The LEDs are wired in parallel.
https://www.amazon.com/gp/product/B00JX1ZS5O/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1