Well, I actually find it quite difficult to find mercury thermometers on sale online, except really expensive ones being sold labelled as "vintage". And even if you do, the amount of mercury per thermometer is miniscule.
With extraction from cinnabar, you get enough mercury for all your desired synthesis in one go.
And since no-one can produce a viable link to actual thermometers ...
But like you point out, the situation can be different for every person depending on where he/she is. I would never ask anyone on this forum where they're from, so it's better to just give a variety of information from different perspectives. One version might work best within the US, another in Russia, one in parts of EU, etc. And maybe some on Mars

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