You can buy Evening Primrose Oil as a standalone supplement; it's usually sold in concentrated, soft gel form. Evening Primrose Oil is also included as an ingredient in some joint support products, EFA blends, and women's health products.
The normal daily serving of Evening Primrose Oil is 1-3 grams. Just remember you want to look for a product that has a high amount of GLA, at least 100mg, not just a high amount of Evening Primrose Oil. It's best to take Evening Primrose Oil with breakfast and again with lunch.
If you are looking for other vegetarian sources of EFAs check out Flax Seed and Borage oil.