It's not how it works. Any particular plant will produce a combination of thc-a and cbd (along with about 20 other cannabinoids). The percentages vary, but every part of the plant will have both. The flowers will have the highest concentration, but even the stalks will have some resin on them.
There isn't one location that has one but not the other.
If you only want cbd, find a source of hemp seeds that are federally legal, which means they will have a negligible amount of thc-a. The better strains will have 15%-20%+ of cbd, and no real thc-a.
Otherwise you get a blend.
FWIW, I make sav's as well. I use shake and popcorn from my grows, and it has both thc-a and cbd. Since I decarb them, the finished sav has thc. BUT, the sav is NOT psychoactive. Some people think there is a benefit to having both. But since it isn't absorbed into the bloodstream there is no high associated with it and you won't test positive.