Amazon has plenty, not expensive. Do a search for Vesa mount for raspberry pi.
@zanewiller seem illogical.
u use them to display tv, so I assume u want the audio.
but u don’t want the audio?
the doc on iframe-ping says it is not active when hidden. so should be silent unless the page being shown uses that module
course if you auto rotate pages, then they will turn on, then off, then on…