I have been researching cabinets for my build and also want ones 18" deep. Home Depot sells a Sandusky Classic Series 72x36x18 but your problem is filling a 60" space if I'm reading your post right. I have not seen any 30" or 60" cabinets anywhere.
Most kitchen cabinet or custom shops today have cad design programs which could design a single or two cabinets together to fill your required space in minutes. This same program downloads directly into their shop cnc router which automatically cuts the parts and drills all the holes for adjustable shelves, hinges and dowel assembly holes. These are usually 3/4" mcp particleboard core cabinets with heavy duty vinyl edge banding. I have had some in my present garage for 15 years and they are durable so long as you don't get them soaking wet.
Glen
