Apple switch spares by part number
Apple appear to have never documented the part numbers of the switches used in their keyboards. Instead, replacement switches were available under Apple’s own part numbers, detailed in various service catalogues. I encountered this by way of RetroConnector’s Apple II Keyboard – ALPS Short Stem 12° Adapter page, which depicts sections from Apple service document. RetroConnector have since uploaded the full documents online for reference.
These documents also yield additional knowledge, such as the meaning of the beige and brown first generation SMK switches (described as “Low Friction”) and the existence of both short and tall stem first generation SMK switches just as with their Alps counterparts. The IIGS entries also appear to offer the final, conclusive confirmation of SMK as the manufacturer of Monterey switches.
The parts list is now on the Deskthority wiki: Apple switch part numbers.