How to get sour cream & onion potato chips flavor?
First things first: If you're trying to precisely replicate the flavor, you'll probably fail. Food scientists put an incredible amount of time, money and effort into developing those flavors and have ingredients and equipment that we don't have access to. Often, the flavors themselves are byproducts of industrial processing, and they've been combined in a way to make them pleasant. So if you're looking to get that exact flavor in your dip, you're going to be disappointed. If you're really just looking for a ballpark approximation which might be a little closer than what you've got now though, you've got a good shot at it.

If I were you, I would first try using dehydrated or freeze-dried green onions or chives which can often be found in glass jars in your grocery store. Mix them with your dip or make them into a powder to toss with your chips. Perhaps pureeing a product like chive cottage cheese which is made with dehydrated/freeze-dried chives might get you there. For the more industrial products, you'll have to look on the internet. Commercial chips almost certainly use sour cream powder (among other flavorants you probably can't find on Amazon) in their sour cream and onion chips. You could even try some sour cream and chives powder to see if that gets you closer, with less work.

Good luck and happy dipping!