I see countless posts like this on the internet... Here the best advice I can give you.
You'd be surprized how much information is in a field guide. You can pick up a copy of Stebbins, or check out this site
www.californiaherps.com. I seriously doubt any serious so cal herper is going to causually let you in on how to find any of the 3 snake species you mentioned. Due to the ever increasing popularity in field herping, a lot of habitat damage and commercial collection of native herps has transpired. You could probably find some scab who's been shown good spots to herp, yet hasn't put in the time and effort, and is willing to let anyone come herp "their spot". If you want to find mt. kings, pick up a copy of Moutain Kingsnake by Brian Hubbs. If you're serious about rosy boas, join the
www.localityrosys.com forum. They have an anual ARC meeting where they go out in search of rosys.
I mention time and effort.... It really does go a long way. I think if you start herping, and start finding herps on your own. You'll learn that the herpers with more field experience will be more willing to give out information once you've "paid your dues".