This really is a personal preference. Lots of guys will get the wire shelving from any home improvement store. Those work, or you can use kitchen cabinets, or premium cabinets for race trailers. Do a search on shelving/cabinets and you will get a ton of answers. I'll try to post some pictures of trailers that I have had.
You can try the following as well...
pitpal.com
pitproducts.com
moduline is another brand that you can search for
Good Luck!