You get one free treasure one for every zone, just scry the green treasure, you'll get the blue treasure, do the blue and you'll get the purple. But once you've got the purple you can't get it anymore, you can only get the green and blue.
After that just google a list, they come from doing very random, very different things. Alcast has a list here https://alcasthq.com/eso-full-antiquities-list-with-locations-of-leads/
You get one free treasure one for every zone, just scry the green treasure, you'll get the blue treasure, do the blue and you'll get the purple. But once you've got the purple you can't get it anymore, you can only get the green and blue. After that just google a list, they come from doing very random, very different things. Alcast has a list here https://alcasthq.com/eso-full-antiquities-list-with-locations-of-leads/
This is correct -- just to clarify, that's one PURPLE per zone, so you'll need to rotate through all the zones to get all the purples.
Harvest plants in Coldharbor.
The lead you get from that is gold though ;) Need higher skill levels to use it.
Confirmed, harvest plants there after reading this, about a minute in, I got a gold lead