You might want to consider taking out a subscription to
Antique Radio Classified, and placing a want ad there. I wouldn't be surprised if some of their subscribers have NOS WE 101D's they would be willing to sell at reasonable prices.
Also, you might want to consider trying to obtain some of the later version WE 101D's that were issued in a more modern domed bulb style, rather than the original tennis ball style. A WE datasheet issued in 1941 for the newer version of the tube states that:
This tube replaces the D-86326 tube and has been assigned the old code number 101D. It includes an improved filament, a new mechanical design using transverse mica supports and is mounted in a dome type bulb. The electrical characteristics are essentially the same as for the D-86326 tube.
Regards,
-- Al