Hi Ethan! As of OS X 10.10 (Yosemite), iPhoto is no longer a bundled application and is officially unavailable from the App Store. As you noticed, the application has been superseded by the Photos app.
The following steps are a bit of a "hack-y" method that might bring iPhoto back for you:
Hi again Ethan! Did the steps I provided for your work to bring back iPhoto? Please let me know!