The regular blue motifs based on player races, like Breton, are randomly located in containers throughout the game world. But are most likely to be found in furnishings like nightstands, desks, dressers, etc. So you will likely need to go into sneak mode and steal them. Note that you can sneak and look in an open piece of furnishing with no penalty, even if seen. You actually have to remove an item and be seen by an NPC to commit a crime.

No need to farm them. People have lately farmed furnishing blueprints and those motifs were farmed as bycatch. You can find the blue ones in guild stores for <100 gold and the purples for ~500 gold.