Strictly speaking, there is one copy of esxA and it is found in the ESX-1 locus. That said, there are 4 other ESX loci, each with a gene homologous to esxA, as well as 6 or 7 other esxA homologs that are not part of an ESX locus. esxA is also very similar to esxB, which is next to it in ESX-1.
Here is an analysis that came out not long after the genome sequence and it is a good place to start: