From speaking to the WE folks, they are temporarily not manufacturing due to a facility re-location.
FWIW, 2 manufacturers of tube amplifiers I communicate with on a regular basis prefer the current generation of WE 300B tubes to NOS versions. This doesn't infer they are "better" only that some people like the contemporary sonics.
The scarcity of old WE 300B tubes has no doubt contributed to their legend and outrageous prices. I've only heard 1 pair and thought them quite ordinary in fact.
YMMV