It's legal to use gear and to possess quantities reasonably within those amounts required for personal use. It's illegal to sell or to provide to others which mostly makes it illegal to buy since you'd be abetting a felony unless you buy from somewhere such as Greece where it is legal to sell or you buy from someone who is licenced.
You can also bring personal use quantities through customs since it's all legal but it'd still be a felony to give any away to others.