The Nikon’s AF-S NIKKOR 500mm f/5.6E PF ED VR Lens (Pre-order at Amazon, B&H Photo Video, Adorama, Focus Camera) is one of the best selling lenses from Nikon. After it was announced in late August, 2018, this lens is still out of stock everywhere. You can take a look at in stock tracker of this lens.
According to NR, The Germany NPS website said Nikon is only producing 1,000 units of this 500mm f/5.6 E PF ED VR lens each month. So that’s why this lens is always out of stock everywhere.