VAN's subcontracted the spar build-ups(using kit parts) to Phlogiston Products in Oregon for what most call "Vans built spars".
http://www.phlogistonproducts.com/Photo-Gallery.html. While it does provide some additional corrosion protection typically applied to aircraft extrusions in commercial aircraft, alodining and priming as adequate for our needs on RV's. I like the easy identification of a Phlogiston spar when doing inspections, as they are typically flawless. There are a couple different anodize processes, Chromic or Sulfuric acid being the most common. You may reach out to Phlogiston and see who they use as a vendor, but all can do similar work. I use a local vendor in NC for my day job stuff, but the west coast has several big ones that support the jet MFG world and can handle long pieces. Hytek in Washington state is well known...get out the checkbook.