The BME280 is not available from any of the normal retailers (Mouser, Digikey, Arrow, etc).
Normally, when they do not have stock, they accept backorders, and can give an estimated ship date.
However this time, they are refusing to take backorders, for example this is the message on the Digikey website:
"Due to temporary constrained supply, Digi-Key is unable to accept backorders at this time."
Have Bosch stopped making them? Should we redesing products to use different sensors, or will they be available soon?