If you plan to miter the corners and glue/pin-nail the pieces together, I would recommend purchasing the lumber locally in one trip, then cutting and assembling it on site.
We can certainly supply similar components, such as finished end panels, fillers, or millwork, but if you expect to make several modifications during installation, buying the material locally will likely be much less expensive because shipping is not a factor.
Floating shelves are not a product category we have focused on. I like the concept, but there are many inexpensive existing options that serve that need well, so we have not pursued them extensively.