There are many pallet rack and material handling suppliers who specialize in used stuff. If you go by and visit them, they usually can come up with some odd size stuff they are eager to get rid of for cheaper than the more "normal" sizes.
I got this setup from a used material handling company. It was totally odd to them, as it was all they had, Interlake brand, (3ea) 14 ft uprights, and (24 ea) 8 ft beams. The odd part is the beams are "lightweight" and are open on the bottom. They won't hold as much, but they still are good for 1500 lbs a shelf. The inset lip for the decking is only about 1" deep rather than the usual 1-7/8", and they are 42" deep total depth, which again, is odd.
I decked it with various things. A couple of shelves have 2x6's cut to length (they stand proud of the top of the beams by a 1/4 inch or so), one shelf is done with scrap 5/4 deck board (perfect thickness), several shelves are done with 1' thick rough cut from pallets that were designed to handle 55 gal drums.
Gotta get creative.
Charles