Replaced hard drive, now Itunes is missing and I can't install latest version how do I reinstall my older version?

My hard drive failed, Apple Genious replaced hard drive and reinstalled everything? from my Seagate backup drive. Now ITunes is missing, and I can't reload or upgrade as newest Itunes is not available for my computer. Nephew upgraded from original Tiger to Leopard a few years ago, but I always had Itunes, what is going on, before I call Apple again?