Well I could suggest going to the offical web site which sell the 3 albums, but the dang linkain't working for me (get a lame white screen) meaning that they to good for my cheap browser lol. If all-else fails, you could check amazon (my reviews are there :Spin: )
...or if you mean specifically which songs, then those would be As Light Is Our Darkness (from The Dark Discovery), Words Mean Nothing and The Shocking Truth (from Solitude,Dominance,Tragedy).
You can practically find them everywhere...just tell your cd store to order it from your country's distributor.
They aren't the same versions....especially Words Mean Nothing is a lot better They're one song,it's available on the limited edition and they don't have a connection or concept of any sort as far as I know,since the songs are from separate albums.