California has about half a million residents per assembly district; the number of registered voters per assembly district is about 300,000. Overall, California has a 60% vote share for democrats, or on average about 60,000 more democrats than republican votes per assembly district. Assuming that what you mean by "single issue voters" is votes per republican, then on average if all CAguns members by coincidence lived in a single assembly district, they would probably not even swing that district the other way.
Now in reality, that calculation is wrong. The biggest reason is that some state assembly races are decided by smaller margins. So if we could identify one of these swing districts, and make all 37,000 CAguns members sell their houses and move there, we would have a chance to decide maybe one district. That would not change the majority in the state legislature at all, but it would be fun. Note that such a plan was proposed decades ago: to have a few hundred gun people move to Alpine county (population of the whole county: about 1200). There they could swing the election for sheriff, DA, county supervisors, and school board (note that Alpine county doesn't even have a high school).
But there is another factor: Roughly a third of all gun people in California (between a quarter and a half) are democrats, not republicans. While they may be single issue voters, they would probably not vote for the candidate you would like.
The salvation for California gun rights does not come from electing republicans. It requires convincing democrats that being anti-gun is pointless and ultimately damaging. Being obnoxious towards democrats does not accomplish this task.