Merkir's Exotic finding guide: (collection/summary of others' advice)
1. Make sure your ship has an Economy Scanner.
2. Travel to Wealthy systems only. On the galaxy map these have 3 stars next to the economy with descriptors like "Opulent", "Flourishing", "High Supply", etc. Wealthy systems have a 2% spawn rate for exotics. Lesser systems have 1% or 0%.
3. Use the "Find Trading Post" function from the bottom menu (only available with Economy Scanner installed).
4. Travel to the Trading Post and keep watching all the NPC ships until you spot an Exotic. My understanding is that there is only ONE type of exotic created for each system. Once you see it, that's the one that will keep spawning. So if it's not an exotic ship you want, travel to the next Wealthy system. I rejected about 8 exotics before a Squid finally appeared.
5. (Gamey) To save time, you can repeatedly reload from last save while at the trading post. This spawns 5-7(ish) new ships on each load, a little faster than waiting for new ones to turn up naturally.
Enjoy!
I was doing this while jumping towards the Centre, choosing only wealthy systems. I'm just 150 kLy away now.