Same happened to me but I found a link that helped me re-install it. (couldn't find it now for reference)
Try looking for it in the Mac App Store for download. If it's not there, try creating a new user account on your Mac. Log into the Mac App store using your iCloud info, then look for it again in your purchases. It should appear under the purchases list. From here you can download and install it again and it should be available in your main user account. At this point, you can delete the new user account. iPhoto should be available now.
This trick worked for me. I hope it works for you too.