These units use the HP 92295A toner (same as the Laserjet II and III). Its discontinued from HP, but there are plenty of cheap clones out there. Parts are readily available for the printers as well. The two weak areas are the fuser and AC power supply. Both can be sourced cheaply online.

Info here: https://www.rheinfeld.de/andreas/laserjet50.htm

The only real difference between the HPs and the Laserwriters is the case plastics and the formatted board. the HPs have LCD displays too. Both printers use the Canon SX engine.