My question is: where did they go and where could I possibly find them?
The types called "Hirose Cherry MX …" were made by Hirose Cherry Precision (AKA "Cherry Japan") in Japan.
Nobody knows how this started. The early Cherry switches (M5, M6, M7, M8 etc) had various keycap mount options, and Hirose's own M8 switches had a different mount again. When the MX series was introduced, the Hirose version (originally branded "HCP" instead of "CHERRY") continued to use the same keycap mount as found on Hirose Cherry M8 switches, instead of the new MX mount.
I've contacted Hirose (now HST — Hirose Sensing Technology) to find out anything I could about their switches, and they've seemingly not found anyone willing or able to tell me anything at all; that proved to be a dead end.
It has been claimed that the earliest MX switches were not colour-coded, which might account for some of the clear switches in the pictures: they're just really old switches before Cherry started adding dye to the plastic for visual recognition purposes. (This has never been proven and photographic evidence is still notably absent, as are all the relevant Cherry catalogues that would indicate when switch colour was introduced.)
The rest of the variants (Alps mount, yellow etc) are a mystery, as the chap who took those pictures (Brother Dragon, with an impossible-to-remember forum name) has never knowingly cited the source of any of his switches; they might be one-off production runs or product samples. I've found proof that Cherry allocated country-specific part number sub-series that might have been used for some of these, but no actual codes. Only the Hirose switches are known to have been used in production.
It would be nice if a fluent Chinese and English speaker could talk to Brother Dragon and find out more, as attempts to communicate with him via Google Translate have all failed miserably. There's a lot that we could learn from the Chinese-speaking community; we just need people who speak good Chinese
and English to talk to some of these guys and find out more about what they know. I've learned a few things from alps.tw via Google Translate, but it's a real headache.