Do they come from combat zones as drops or is there a way to get them via quests or NPC purchases?
Tech I BPOs are generally seeded on the market by NPCs in NPC stations. There do exist some legacy tech 2 BPOs, but the process used to create them can no longer be employed. Tech 2 items are now ordinarily created as blueprint copies by the process called ‘invention’. Other BPCs can drop from various sources, or be purchased from loyalty point stores, depending on the type you are looking for.
Well there is a mummy BPO and a daddy BPO and they get together for some sexy time, and then another BPO is born
BPOs do not drop, they are bought from NPC sell orders.
What the devil is a “quest”?
an awful thing that players from wow and other mmos think they will find in this sandbox game
So add the following.
BPC’s do drop from certain NPC kills, or from NPC mission rewards or events.
but OP’s question was about BPOs, not BPCs
Probably because they exist in EVE.
Just like dungeons exist in EVE.
Quests indeed exist in EVE. I know that Katia Sae was on a years-long quest to visit every system in EVE. Quests in EVE are, however, are most usually given by players to themselves and never by NPC agents.