Well, as the OP, I see that I've opened up quite a discussion.
So, in summary (so far) it looks like we've established for future readers and scope restorers the following;
1.) 6DJ8 are scarce and expensive, but not quite unobtanium, yet... as of June 2021.
2.) Russian 6N23P tubes have some definite applicability, but may suffer from reliability and lead time issues. Compensations are required, and available - for a price
3.) 6BQ7 is a viable option, but only with caution in every case since Tek may have pushed particular applications beyond 6BQ7 safe operating zones (Thanks Prof. Lee!)
4.) Some guys on this forum have lots of ECC88 just wasting away in THAT box, and doggone it they haven't sold them to me yet. :-)
5.) I reckon I need to see the little woman about an advance on my tube purchase budget, re; item #4
Future readers and scope builders of tomorrow, we salute you!