Like the FE 24-105 F4 & FE 400 2.8 GM, there will be a huge demand for both lenses. Don’t expect either lens to appear on shelves any time soon. The only way to get either is to place an order as early as possible.
If you live in the U.S., I suggest ordering from B&H Photo where your credit card is never charged until your lens is in stock! If you’re outside the U.S., Amazon is probably your best choice for fastest fulfillment.