I've bought and sold quite a few domains and I think you just reached out to your target audience right there. My guess is anyone buying a .io is doing it most

I've bought and sold quite a few domains and I think you just reached out to your target audience right there. My guess is anyone buying a .io is doing it mostly because nothing else was available, I don't see a huge demand for them. I wouldn't expect much of a price and it probably won't be worth it to make a large effort to find a buyer. Perhaps offer them to people at HN: whomever proposes the most upvoted idea and makes a $10/50/100 donation to a charity (you could choose or they could).