How do you find blueprints?

[Andargor]

Talking to NPCs? I heard rumors of shipwrecks, but I have found none.

Are blueprints for rare items that are not sold at stations?

EDIT: I'm in multiplayer if that makes a difference

[Vice]

There are two ways to retrieve build templates. You can pay to request information from AI/NPC ships or hunt for data drives (sensor stations work best). Blueprints can be for rare/hard to find items (including shield modifiers, which can only be built), but can also be for more common items (building can often be much cheaper than buying, so it can also provide a cost benefit).

[YaroslavUSSR]

Talking to NPCs? I heard rumors of shipwrecks, but I have found none.
Are blueprints for rare items that are not sold at stations?
EDIT: I'm in multiplayer if that makes a difference

You should deploy sensor stations near planets/asteroid fields/asteroid caves/nebulae and look for purple dots on the radar or sometimes ask NPC.

[Marvin]

Also, hire a science officer. Whenever you enter a new sector, he will inform you of things nearby (in the same sector). You can then deploy a sensor station. And don't forget to check the info on the left-hand-side of the sector map.