Depends what your looking for - I now get my sauce from amazon. I have been using Jersey Fresh Tomatoes Fattoria Fresca from amazon and I like them very much.http://www.amazon.com/gp/product/B00F9TCIL6/?tag=pizzamaking-20
I plan to try these next, they are highly regarded- Sclafani Crushed Tomatoes http://www.amazon.com/dp/B00F9TCIQG/?tag=pizzamaking-20
Before switching to the Jersey Fresh Tomatoes I was using 6 in 1 crushed tomatoes from Mona Lisa restaurant on India Street (as mentioned above). 6 in 1 is great but I like the Jersey Fresh Tomatoes better.
Cheese has been a challenge - I have not found anything I'm in love with (local) and I have look and tried for years. I did join the Kansas City Barbecue Society (KSBS) so I could get into restaurant depot (RD). I found some passable cheese but it only came in 5 Lb blocks. They also have good sauce but only in #10 cans (too big for me).
Flour, it depends on what you want to use, if your looking for Bromated Flour you will need to mail order, (and get your wallet out) if not, you have options. There is a nice guy that runs New York Bakers - you can arrange to pick up you flour at his shop and avoid shipping - lots of choices http://nybakers.com
I usually mail order my pepperoni (Vermont Smoked Pepperoni) from Amazon but I have found some good sticks in Little Italy.
After that you have great choices for everything else you might likely put on your pie, just about anywhere in San Diego.
Hope that helps and if you find any good cheese -- by all means, please let me know.....