The best way to get those unique pictos is through side activities scattered around different areas. You'll want to check out gestral village first, where berrami hangs out in the bazaar looking for his expedition journals - bringing those back gets you the colour of lumina which is pretty neat. While you're there, keep an eye out for eseda lurking in the alleys, taking him down opens up his shop with some interesting stuff.

If you're exploring the ancient sanctuary area, there's this whole thing with gathering three glowing rock crystals around stone wave cliffs that'll get you the auto shell picto, and over in the red woods you can find this mysterious fountain where donating some chroma gets you a recovery picto. Actually, something interesting about these pictos is you can't just buy them or find them lying around anywhere else.

Once you make it to the stone quarry in act 2, there's this fun musical challenge with the trobadour that rewards you with the healing parry picto. The npcs around these areas usually drop hints about these opportunities, so it's worth chatting with everyone you meet. Some of the tougher optional bosses like jujubree can drop special ones too - beating him gets you the demonam which works great for gustave or verso builds. Just remember that a lot of these special pictos are hidden behind puzzles and optional fights, so take your time exploring places like the esoteric ruins maze, and you'll find them naturally as you go.