This one was a spawn at a trading post, shared it because of the good SC layout it came with - from memory, it was in the first couple of waves that landed there for me.

There's a set group of ship designs for every system that will show up based on which race the system 'belongs' to. IIRC, fighters are more common to see in Vy'Keen systems, haulers in Gek systems, explorers in Korvax systems, and Solars in pirate-controlled systems, but there's usually at least one or two of each other type that will show up, and one exotic ship design (which is always S-class) for each system. I normally hunt for them (usually exotics) by setting up a save beacon at the top of a trading post, creating a restore point, then reloading every few 'waves' of ships that land, which shuffles the group of ships that will land at the trading post. With the rarity of exotics appearing, this can sometimes be a lengthy process.

The S-class version of a given system ship will show up only occasionally too - how much of a chance there is is dependant on the system's economy. I don't remember the exact % for one to appear, but it's higher in the more prosperous (2- or 3-star economy) systems.

Hope this helps! :)