Hi, welcome to RTA!
As far as contacting national parks and such, I know there are links to the NPS campgrounds on the Camping forum.
This link takes you to the forum regarding camping in the national parks. Once on that, the first post lists all the national parks with campgrounds, so you'd just click on the NP you want. Once you're on the NPS site for the campgrounds in that park, you can get to the home page, find lodgings, etc. (If there's an easier way, one of the mods will let you know.)
Should you go from SF to Malibu, you can use CA-1, the Pacific Coast Highway (PCH). There are some beautiful sights and, going south, all the pull-outs will be on "your" side of the road.
Congratulations (early) on your retirement. I just retired (from teaching) a year ago; love to be able to travel when I want to rather than focusing on school year vacations. That's a definite perk to retirement!
Donna