You can certainly try Googling but your yellow pages will do the trick as well. Look under landscape supplies or soils.

FWIW, if you need mulch, soil or other amendments in any kind of quantity, bulk providers will always be far cheaper than any kind of bagged goods.

Here is a link that might be useful: a few sources - scroll down to #3

Tree trimmers are usually glad to dump their load in your driveway/yard ... for FREE .... saves them the tipping fee at the dump. I have been very happy with this mulch ... both in pathways and planting beds ... and earth worms seem to love it.

Call some arborists and tree maintenance companies. Shredded and chipped trees make fabulous long-lasting mulch.

Just be careful to judge how large that truckload is. I often give the supervisor ten bucks to get that load in my driveway. Most loads I see hold about five cubic yards.
That's a good bit. Do you have help that can help you move it off the driveway. It never fails that they block the garage door. Be sure the car is out. I speak from experience.

Check out some of the trash/dump transfer stations. They will give you stuff for free that is a mixture of tree trimmings and leaf litter that has been thru the grinder. I think there's one in Cypress or Buena Park that does it.