Forum Discussion
They used to be available via the Accessories page https://www.roku.com/products/accessories, but Roku stopped offering them a while ago. (remembered seeing another user requesting this a few months ago).
You should be able to use any bluetooth or wired earbuds (3.5mm jack) you want to with your Roku devices. (I have used many different ones and all worked fine).
If you need some cheap ones, you can look at the Maeline 10-pack ($7) https://www.amazon.com/Maeline-Bulk-Earbuds-Headphone-Plug/dp/B08BSZ1Z86/ref=sr_1_16?sr=8-16
Over the years I've used many different earphones on MP3 players, phones, Roku's, etc. I've settled on the Panasonic Ergofit earphones. They fit my ears well, sound very good, and are reasonably priced (currently under $10/pair), in your choice of colors. (I seem to like blue.}
https://www.amazon.com/Panasonic-RP-HJE125-A-Wired-Earphones-Blue/dp/B00KZIQH86/ref=mp_s_a_1_6