You can buy them right now, there’s more links in the 18650masterrace subreddit, but here’s just one:
https://srikobatteries.com/product/sodium-ion-18650-1250mah-50a-rechargeable-battery/
However good luck finding a BMS that works for it’s particular voltage range, don’t think AliExpress has any yet.
I haven’t seen any posts from those diy type folks experimenting with them yet. Sodium ion cells just became available within the last few months or so.
Same, I know absolutely zero people who have gotten long COVID. My brother had it kinda mess him up with fatigue for a few months but he’s perfectly fine now.