By default iMovie saves your project files onto the local disk of the computer you are working on. These files can be found within your home (user) folder. While the home folder is cached on the Mac operating system, there should be no expectation that files saved locally will be permanently available. Depending on the version of iMovie you are using, the exact location of iMovie data may be different.
For iMovie 10:
For earlier versions of iMovie locate the Movies folder and each of the following:
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