I had a local metal fabricator friend build cages for my mono amps (see my system pics) using a mesh steel plate that is commonly available. These folks are high-end fabricators, and personal friends, so I could not reccommend them to do the same for others (they'd turn down the job), but you should be able to find a local metal fabricator who can whip up a set for you if you give them some very careful measurements. There are all kinds of metal mesh and perforated sheets that could be used. Price for a custom set would likely run around $100 each or so I'd guess.
Marco
Marco