Nidacore
Nidacore is the only one on your list I've dealt with. They focus on wholesale to manufacturers. Not that they won't sell you materials direct - a boat builder might need a one time shipment so they do work with small orders I think.
The Nidacore panels & resins used to be carried here in San Diego by DMC, but when they went out of business I don't think any other distributor picked up the line, not sure who has it in LA. All of these panels will be expensive unless you're getting a lot of it since it ships on a pallet commercial freight so residential delivery is $$$.
Composite supply companies in SoCal may have these materials in stock if they have a customer using it for production already - or they may special order it in for you. For specific item, it's easier to start at the source and find out what they shipped to which distributor, then call the distributor.
For anyone in San Diego, a handy source for fiberglass materials is
Fiberlay, they sell retail and have a pretty deep catalog of materials. The warehouse is just off of Morena by 5 & 8 intersection.
Cheers
John