Penal Code 288a *is* oral copulation with specified persons.
The full text of all California codes is available at http://www.leginfo.ca.gov/calaw.html
I tried to paste the entire section, but it exceeds Avvo's character limit.
I am unaware of any source for the kind of statistics you have requested.
Make sure you're looking at the right section.
There's Penal Code section 288a [without parentheses] that deals with oral copulation. There are subsections that are for the act done by force, because the victim was intoxicated, age difference, etc.
Then there's Penal Code section 288(a) [with parentheses]. That is lewd and lascivious acts on a child under 14, commonly referred to as the child molest section.