New table -- can't find 18" paver. Substitutions?

Long time lurker, finally joined the club with a large BGE!  Table nest is being ordered so I'm waiting to set it up.  I built a table this weekend but am looking for something to set the table nest on.  Lowes/Home Depot only has 16" pavers and none of the tile stores locally can help (So Cal).  

Any idea where I could find a 2" thick 18x18" paver or another piece of material that can be sized and put into there? 

I loved the idea of a round piece of granite and resting the nest on there, but not sure how I'd go about getting that as the tile/countertop places looked like I was crazy for even asking.  

Any help would be appreciated!!