Rhododendron maximum will grow and bloom in quite dense shade. There is also a variety named Independence or sometimes Independence Day that is either a selection of r. maximum or a hybrid with a maximum parent. Both are late bloomers with the usual drawback of the flowers being somewhat hidden among the leaves. Both will also grow to 10 feet. FAST is more of a problem. Few rhododendrons could really be described as fast growers, especially in an area where they may have to compete with hemlocks for moisture and nutrients. If you're willing to spend the money, maximum can usually be found for sale in pretty large sizes. Check with any of the larger nurseries such as Weston, Russell's, Mahoney's in your area. They may also be able to suggest other possibilities.