How could I learn the speaking patterns of the following groups of persons?

Gangsters in Baltimore have different speech patterns from gangsters in Louisiana.

There are equally as many different speech patterns and accents from different castes, classes, educational background and regions of NYS.

Where does your story take place? Have you given your character from CA. specific characteristics? If not, start there. How old is she? Where did she grow up? Where does she live now” Is she a student, professional, blue collar worker, CA. native or transplant?

You are looking for cut-and-dried answers that you will not find. Avoid clichés,

My father and uncles grew up in the Bronx. My dad spoke with a regionless accent; my uncles were “dese, dems and dose” guys, as my mother kept telling us.

You definately need to be more specific. Generality is your enemy, to paraphrase Stanislavski.
What kind of pimp? From where?
What kind of gangsta? What gang? Bike gang? Bloods? Mexican? Black? There are gangsters from every race. Where from? Oakland? LA? France?
Where in Cali is your girl from? I am from the central coast, and my dialect is distinguishable from that of someone from Norcal, the valley, etc. what part of new york? And remember race enters into each of these characters. Specificity is your best friend when creating believable art.

Pimp: ???
Gangster: LA gang
California: UC Berkeley
New York: Bronx

Watch movies. They are really bad at stereotypes, but unless you want to join a gang…
Or you could read a book with their dialogue in it…

I’m going to concentrate on your Berkley student since I am most familiar with that sort of character. Was she born and raised in Berkely or did she move there from somewhere else? What year is she in? Does she smoke weed? ( the answer is likely to be yes if she goes to Berkely) Has she ever lived anywhere else, and for how long. What is her race? What is her economic background?

Details are where great art lives!