The attached link lists boron content in high content foods together with the amount required for the indicated mg amount. Even if these foods could be consistent in boron content I wonder how many would consume the amount needed to reach even a 3 mg level. Of course it's good to favor boron rich foods but a supplement offers obvious advantages. It's important to remember, boron is a calcium manager like magnesium and K2MK4. They work together to keep calcium from becoming toxic. Now is a good brand that is consistent in quality. I favor supplements minimizing fillers and the usual suspects..soy, wheat, etc. The heart of supplements is form and source. Alpha Lipoic Acid, for example, comes in several forms but R- Alpha Lipoic Acid is the exact form the body makes and recognizes.
https://www.algaecal.com/algaecal-ingredients/boron/boron-sources/