I was sitting around 600 Koroks found and was having a really difficult time following any sort of checklist to find the rest since I would need to check off all 600 that I found before it would be useful for me.
So, I slapped this together to parse a save file from the game to show only the ones that I have yet to find. I also added Locations on there for good measure as they play into the percentage on the map as well.
As you find Koroks/Locations, clicking on them will remove them from the map.
Once a save file has been loaded, the parsed data is saved into your web browser, so you can close the window whenever you like without losing anything. It will also remember any markers that you have removed.
If you would rather use this as a checklist without loading a save file, that option is available as well.
Thank you @marcrobledo for the save game editors much of this code is based off of and @MrCheeze for the their waypoint map which I modified to get the map markers I needed as well as all of their datamining research.