Sorry, I mean just random crashes ships that you might come across when flying around planets that you can land on. I guess, from what I’m reading, is that they just show up.
I've not been able to confirm this since 3.3, but back in v3.1 I was reliably able to find random (non-persistent after re-log) crashed & still smoking ships. The trick was to search areas being circled by Search & Rescue NPC ships you would occasionally find patrolling near the surface. There was one particular System, Ashandras & less so, Sui Xing, that seemed to have frequent Search & Rescue ships patrolling. Every time I found one circling, I'd estimate its search area and either search by Air or SRV. I found a wreck every time, so I figured this is past coincidence, especially since I do spend ALOT of time in SRV's, and it's pretty rare to just stumble on one.
One time the wreck was even surrounded by trespass markers and guarded by Skimmers. I found 3 or 4 one night, and again the next. Each time after a re-log, to prove they weren't persistent wrecks. I never did get around to reporting it on the forums, but I have just dug through my old screenshots - was July 2018, so definitely v3.1.
I'd be interested to hear if anyone still finds Search & Rescue ships over planets since 3.3. I don't think I've seen one since 3.3 dropped. :/