It can be difficult to trace various editions of inscriptions, but fortunately help may be found:
Supplementum Epigraphicum Graecum
Of course you should consult SEG via the indexes. For instructions click here. For a direct link to the SEG concordance click here.
Claros: Concordance of Greek inscriptions
The concordance site Claros allows you to find out quickly whether a particular inscription has been republished elsewhere.
The University of Münster offers an on-line concordance for IG to IG and IG to SEG (Also accessibe via IG site)
A concordance for the inscriptions in Rhodes-Osborne can be found here.