The switches are (formerly) off-the-shelf Hall effect switches by Micro
Switch, type 1A3S. That's an ess not a five.
See the third entry in the picture/table at
https://deskthority.net/wiki/Micro_Switch_SD_Series
I tried searching for that part several years ago and it was
obsolete/non stocked then :( Googling shows a few inquiries on forums
(with no answers) in the 2010's.
So I think the only solution will be a scrapped keyboard - it might be
possible to replace just the Hall sensors but that is delicate surgery
and likely beyond my skills.
