So as the title says.
My country only sells not food-grade, but I found this site: https://www.sproutmaster.com/collections/35-food-grade-hydrogen-peroxide
However, I am unsure if it is wise to trust it.. Perhaps somebody has a trusted website that they buy/bought the 35% Food Grade Hydrogen Peroxide from?
I believe international laws prevent selling 35% overseas. if you're country doesn't sell it It'll be hard to get it at that %, it's dangerous to make it yourself, but not overly complicated. There are multiple ways. I would not suggest making it, as I think you can try and find it in your country, I'm sure somewhere someone sells its for food sanitation in business, as that's where it's most used. check restaurant wholesale suppliers.