I have both Zro and Living Metal available on the galactic market in my current game, despite not having a deposit of either resource in my own space. All you need is for any member of the galactic community to have any amount of a resource in their stockpile for everyone to be able to buy that resource. In this game, the AI found and mined Zro, and I got 40 Living Metal from a trade with the caravaneers. (I still don't have living metal tech though, so I currently have no way to use the resource.)I've never seen Living Metal on the galactivc market unless I had acces to a node myself. I believe the same is true for Zro, but I rarely watch out for it, and it's more common than LM, so I can't be sure.
And, yes, even as Machine Empire or Synthetic ascended I often get the Psionics tech (and then Zro Distillation) with the help of Racket or Curator scientists.
That said, the internal market does require you to find a resource yourself. If you're not in the galactic community or the galactic market hasn't been founded yet, you're using the internal market and need your own supply.
As for making zro more common, one idea would be to make salvaging a psionic entity or fallen empire fleet with psi components give a small amount of zro, assuming this isn't already how it works. Once you have some zro, you should be able to buy more from the market.
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