Building Maple stand need inexpensive wood supplier

We have a great place here in Michigan that supplies a wide variety of woods. I was able to order some very thick quartersawn oak for the tops of my Sound Anchor amplifier stands.

I think it is all about how you conduct your internet search.  I looked for places that supply woodworkers assuming they are likely to know where to source wood.  I looked around just a couple of minutes on the web and have included a link below that might help.  With a few phone calls, you may be able to find somewhere that can source what you are looking for.  Just glancing over the list, I suggest you start with Frost Hardwood in San Diego.
https://www.google.com/search?q=woodworking%20supplies%20san%20diego%20ca&rlz=1C1GGGE_enUS488US488&oq=woodworker+supplies+san+diego+ca&aqs=chrome..69i57j0.13006j0j7&sourceid=chrome&ie=UTF-8&npsic=0&rflfq=1&rlha=0&rllag=32822368,-117173388,6610&tbm=lcl&rldimm=11970610243811531332&ved=0ahUKEwi5kKz1_rrZAhVD21MKHaKUBbcQvS4IcDAC&rldoc=1&tbs=lrf:!2m1!1e2!2m1!1e3!3sIAE,lf:1,lf_ui:10#rlfi=hd:;si:11970610243811531332;mv:!1m3!1d307230.5848711836!2d-117.112376!3d32.855669549999995!2m3!1f0!2f0!3f0!3m2!1i129!2i275!4f13.1;tbs:lrf:!2m1!1e2!2m1!1e3!3sIAE,lf:1,lf_ui:10

Johnson's Workbench, Charlotte Michigan
Some info;

The Longest Running Hardwood Lumber Company in Michigan.
Established in 1909, we are a specialty lumber yard providing access to over 100 domestic and exotic hardwood species, and have the edge with our top-quality plywood and veneer products.
Known for offering a unique combination of hardwoods, plywood, woodworking machinery, supplies, and hardware, our customers often claim they find the resources for their projects through us they can't find anywhere else.
The summer of 2007, founder L.L. Johnson's great grandsons, brothers Mark and Tim Johnson, took over the reins to the lumber mill in time to usher the company into their 100th year of business. Their fourth generation ownership bestowed the company with another notable achievement. Only 3% of family owned businesses in the U.S. survive to the fourth generation.

The also make cuts and for my last project they joined and planed the pieces which saved me a bunch of time and made the project much easier for me to complete.