I don't have the black market facility installed on my carrier, which might make the difference. I wouldn't buy one just for that ability though, since I can store stolen goods without one. Still seems silly that I can't launder the goods directly through the main engines, it's not like stolen limpets can't be used just as well as any other.
I was in a 4-million population anarchy system, hanging around the low-res to knock off miners as the supercruise spawns were pretty poor. The miners seemed to spawn into the rings with small amounts of goods already in their holds, but I didn't see anything better than tritium. Still, for low-population the spawns were better in the low-res than they were in supercruise. Trying to find some higher-population anarchy systems that have decent rings, but EDDB's body search is down right now.