For sale is a single WE Western Electric 421A vacuum tube, halo getter version, date code 6652. This one tests near NOS. RESULTS (side one / side two).
Western Electric Type 421A Dual Power Triode Tube, Good
This is a used tube which tests strong. It tests at 52 and 58 were the minimum is 40 for each plate on my military TV-7D/U tester. It should be great for your project.