chances are, if they are broken, they are OEM BMW springs original to the car.
You can buy them from the dealer, and spend tons of money, or shop around online, and buy a set of aftermarket springs.
If you are looking for the OEM ride hight, and have no interest in lowering the car, try your local pick'n'pull junkyard to buy a used, but good, set.
Patrick ///99 540iA///BMWCCA#465139
98 328i hellrot (sold)