It's virtually impossible to clearly establish an accurate count of gun owners.
Maybe the number of new sales from a certain point forward, if the individual state registers all FFL transfers (like CA does), or new residents moving into the state (like CA does), but even then that doesn't take into account any guns owned prior to the "start date" of FFL transfers of private sales, let alone family transfers not registered, or unlawful transfers.
Doing a poll and then extrapolating numbers? Really? Dream on.
CA has seen some huge sales of new firearms in recent years. Some years came close to seeing almost 1 million guns sales recorded. FWIW, the state didn't start archiving sales of long guns until 2014, so who knows how many of those are in owner hands?
Info post San Bernardino shooting incident:
https://www.sacbee.com/site-services/databases/article53245015.html
Some 2015 article info on gathered "statistics":
https://www.revealnews.org/article/in-california-handguns-enter-2nd-decade-of-rising-sales/
The "number" of lawful gun owners in CA is usually thought (estimated? believed?) to be around 8 million people, but that number could easily be an under representation of the actual number of
lawful gun owners. Might be off a bit in the other direction, too, as some occasional "buy back" events have revealed a lot of older guns being disposed of by family members who are cleaning out guns owned by an older generation. I saw back's of SUV's, trucks and car trunks filled with older shotgun and hunting rifles at one buy back event I witnessed. (One guy brought in more than 90 guns he just decided he didn't need to own anymore.)
Now, if we're talking about the number of actual guns in CA? Good luck. The guns owned before the '68 GCA, and then much later the state first starting to register and archive sales, is unknown. Back then it was possible to send a money order to a dealer to buy a M1 Garand or M1 Carbine and have it mailed to you. I remember my father buying a M1 Carbine that way, for $13, from an ad in the back of a gun magazine. (No, I
don't own that great example of a .30 Carbine, but I fondly remember trips to the backwoods where we'd shoot it.)
I'll offer that I've learned of a LOT of new guns owners numbered among younger CA residents in recent years, and they weren't just buying one gun, either. They were coming back to buy more when the 30 day limit for a single gun purchases had passed. Lots of new enthusiasts and owners who want to be able to own a firearm for defense.