If the App Store doesn't even let you buy it on 10.9, you could install 10.11 and use that to buy and add it to your purchase history.
You could insert the "Install Applications" disk and use the app Pacifist (free) to extract iMovie from the contents. While not an ideal solution as you would be stuck with the version of iMove that shipped with 10.6, it would be free. Should you choose this route, you could also browse support.apple.com/downloads/consumersoftware to download any supplemental updates from there and again use Pacifist to install them, should the installer complain about your using 10.9.Thanks for your suggestions, I appreciate it. App Store doesn't let me download or buy iMovie. I do have the original installation disks but it's not possible to install the apps from the DVD to Mavericks.
Once the app is in your purchase history, if you attempt to download it on 10.9, you should see a popup like the one below from my Mac running 10.9.I actually have El Capitan installed on an external hd; been testing it a few days. But does it help if I buy iMovie on El Capitan and add it to my purchase history? I mean, the version of iMovie that is available in the App Store seems not to be compatible with Mavericks. Or do you mean that it will become available to download on Mavericks if I buy it on El Capitan?
You're welcome, I'm glad it worked.Yes, it worked exactly like you said. Thanks a lot, I appreciate the help. I got iMovie version 10.0.5 on Mavericks.