An idea used for lumber racks may be applicable to your needs: In the
2X4 supports secured to the wall, drill* 13/16" holes at desired shelf height. Insert appropriate lengtsh of 1/2" iron pipe and rest the shelves on top of them. The holes can be angled slightly to have the shelves slant downwards towards the wall if desired.*Check the size before drilling, I believe 13/16' gives a snug fit for 1/2" iron pipe but my memory is not what it used to be. If you want, you can use 3/4" pipe for more strength, that would probably require a hole in the 1 1/8" range or thereabouts.