There's really no good stats on SF car jackings, unfortunately. The SFPD crime data is too coarse to discriminate carjackings from other car theft. I think the best you could do, unfortunately, is comb news stories and try to get a sense of the frequency. A quick google search turns these up:
Dec 22: https://www.sfexaminer.com/news/crime/man-shot-during-attemp...
Feb 6th: https://www.mtdemocrat.com/news/assault-carjacking-suspect-a...
Feb 21st (and mentions a second Nov 7th): https://www.kron4.com/news/bay-area/armed-carjackings-near-s...
Mar 1st: https://sfstandard.com/criminal-justice/teens-carjack-couple...
You could perhaps automate something to give you a proxy statistic. Hell, it may end up a better statistic than what the SFPD has.