It can be difficult to trace various editions of inscriptions, but fortunately help may be found:
Supplementum Epigraphicum Graecum
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.
Click here for Concordances for CIL with earlier editions and addednda and corrigenda