You probably are looking for something like these...
These are from
Western Power Supply.
Tires catalog,
pages 294-295.
edit to add... just noticed they don't list pricing. Call SCCA and ask for a price/availability check.
You could probably also find them in
Parts Unlimited and
Tucker (formerly known as Tucker Rocky, aka Drag Specialties).
Most local moto shops can order them for you.
Some, like Santa Clara Cycle Accessories (SCCA), may even take 10% off and not charge shipping.
If your looking for something smaller you might consider buying the metal and having a local welder build it for you.
Also... SCCA has a wall of tires on the industrial shelf racks (w/o the shelves). Their shelf crossbars are perfect depth to hold tires. Then you could put shelves on upper levels for additional storage.