This was such a tough product to find. I took a flyer on this company when I built my wash bay in earlier 2016. These are custom made to our spec. Keep in mind these are insanely high quality stainless steel, hence the cost. These will last longer than you.
I've listed the most common sizes, but I can have them made in pretty much anything you want including slightly less expensive T430 or marine grade T316L stainless steel. Floating designs are also available(about 2 times the cost). Email me at firstname.lastname@example.org if you need something different.
The size I have in my garage is 8" deep x 32" wide. I was able to mount the brackets directly to a stud to ensure they never move. 8" is the perfect depth for gallons from Adam's, Griot's, Chemical Guys, etc. If you are a big CarPro fan, you may want to go with a 10" depth. CarPro gallons fit on the 8", but there is about a 1/2" over-hang.
Shipping on these is complicated, so we will handle these just like Saber cabinets. Budget 25% of your shelving for shipping. e.g. $500 in shelving will cost about $125.
My guess is 8" x 32" will become commonly ordered, and Stainless Supply will begin holding more stock. But, generally these are built-to-order, so expect several weeks after ordering.