The best way to find is use the Search option(you might have tried it before.) Generally the PST files are stored in different folders depending on OS, I have XP installed and the Path is “C:Documents and SettingsUsernameApplication DataMicrosoftOutlook”
try this if you were using XP as your old OS.
or find is the best option or a similar path but you need to explore all Microsoft folders & sub-folders. I remember that in windows 2000 professional, the path was something crazy like a 128-bit address.
The PST’s there, but you need more time to explore.