I purchased my wire shelving (Closet Maid) from Home Depot and had the same problem with my mini bolts falling through the slats. I happened to have a roll of that plastic canvas for needlepoint, and was able to cut that up into strips and laid it down on the shelving. Works great and the shelving has air circulation! So it's all acid free.
I have not been able to find any more of that plastic canvas by the bolt tho. It was so many years since I had purchased the last piece that I no longer recall where I got it from. But it solved my shelving problem and made me very happy...!!!