Buy a bottle of club soda. If you check the ingredients, it doesn’t have corn syrup (or sugar). It’s carbonated water.
Then buy a fruit juice of your choice. Check the label on this. Make sure it’s just fruit juice or if they’ve added sweetner, that it’s sugar and not corn syrup or high fructose corn syrup or “fructose”.
Then mix the two. How much you use will depend on the fruit juice you use and your taste. For instance, I’m using blueberry right now and that’s pretty strong, so I use about 1/3 juice and top it off with club soda. And I may have to add a little sugar for sweetness as the blueberry juice I’m using is all natural and doesn’t have sugar either.
If I was doing lemonade it would be mostly lemonade with only a little soda for fizz because lemonade isn’t as strong as blueberry juice.
At some point I’m going to be compiling a list of foods with corn syrup and those without. And easier reference than trolling the aisles and reading a bunch of labels.