A non-Rostered handgun can be transferred between two CA residents.
So if someone in CA already had one he could sell it to you.
Cops can buy nonRostered handguns and can then transfer them to you too.
A non-Rostered handgun can also be transferred to you from a lineal family member (grandparent/parent/child/granchild) or be inherited/willed without concern from Rostering. Some CA FFLs don't know this is legal but it is per 12078PC (paragraph c or d, can't remember.) Uncles, cousins, brothers, etc. don't count. If you had a grampa in Texas he could buy you a nice Christmas gift and send it to your local FFL (ideally with a gift letter that can be copied for FFL's files): the FFL enters an override in the DROS system saying something like "12078PC Roster-exempt intrafamily gift".
Some non-Rostered pistols can be modified into single-shot pistols or single-action revolvers that are (if dimensionally compliant) Roster-exempt per 12133PC.
I expect the safe handgun list to come down in the near future due to a variety of reasons - one of the biggest is that gives LEOs the right to buy nonRostered handguns for personal use.