I could acquire some new old stock (2007) of Maxwell BCAP0650 ultracaps for a very good price. First electrical testing tells me that they are in very good condition, despite the fact that they are quite old. Only caveat is that the are all of the weldable type, without threaded mounting studs.
I have ~ 800 of them, just for kicks: their combined short circuit current would be more than 2 million amperes
If anyone has the right tools (I'd say a TIG welder should work) and is interested, please let me know. I'm also selling them in my shop: https://www.keenlab.de/index.php/product/bcap0650/