Historically, users could find updates like 10.10.5 through the "Software Update" mechanism in the Mac App Store. This process automatically downloads and installs the necessary files, including the DMG, in the background.
OS X Yosemite 10.10.5 was the final major stability update for Apple’s 10th Macintosh operating system release mac os x yosemite 10.10 5 download dmg