10 days ago - Sleipnir - Direct link
You just need to unlock the items by discovering them first. So, if you unlock the Arboretum node in the Saga research tree, you should have access to tree seeds and such. Keep in mind, you need to keep playing that realm where you unlocked the research. So, you'd want to unlock it, open the overworld map, select an ocean tile, and then click settle. Instead of going to main menu and starting a new game.

Let me know if that works!