As an update, solenoids are now available to order! They work on any xwhatsit Model F or xwhatsit beam spring keyboard! Each solenoid requires a solenoid driver too.
More details here: https://www.modelfkeyboards.com/product/xwhatsit-beam-spring-or-model-f-controller/
The xwhatsit controller supports buzzers directly and some types of solenoids through the solenoid driver add on board.
admin edited answer
A Deskthority user has added a solenoid to his Brand New Model F Classic Case Keyboard https://deskthority.net/viewtopic.php?f=62&t=23707&p=462600&hilit=f62#p462600