Are you looking for like a woven wire mesh material ? I believe this would probably only come in squares as opposed to the diamond shape that you are looking for - some squares can be seen here:
http://www.bwire.com
If you absolutely must have the diamond shape - try possibly either Grainger, or Mcmaster Carr....
I think the diamond shape is less transparent, and in another sense, more expensive - but they should have it here: http://www.mcmaster.com