I was rooting around the internet and stumbled upon the FINAL official download links for older versions of Google Chrome. I found one and just changed the OS identifier in the link string to find the others.
I did not find links for anything older than OS X 10.9.
Mac OS X 10.9 Mavericks: https://dl.google.com/dl/chrome/mac/legacy10_9/GGRO/googlechrome.dmg
Mac OS X 10.10 Yosemite: https://dl.google.com/dl/chrome/mac/legacy10_10/GGRO/googlechrome.dmg
Mac OS X 10.11 El Capitan and 10.12 Sierra: https://dl.google.com/dl/chrome/mac/legacy10_11/GGRO/googlechrome.dmg
Mac OS X 10.13 High Sierra and 10.14 Mojave: https://dl.google.com/dl/chrome/mac/legacy10_13/GGRO/googlechrome.dmg
Mac OS X 10.15 Catalina: https://dl.google.com/dl/chrome/mac/legacy10_15/GGRO/googlechrome.dmg
I did not find links for anything older than OS X 10.9.
Mac OS X 10.9 Mavericks: https://dl.google.com/dl/chrome/mac/legacy10_9/GGRO/googlechrome.dmg
Mac OS X 10.10 Yosemite: https://dl.google.com/dl/chrome/mac/legacy10_10/GGRO/googlechrome.dmg
Mac OS X 10.11 El Capitan and 10.12 Sierra: https://dl.google.com/dl/chrome/mac/legacy10_11/GGRO/googlechrome.dmg
Mac OS X 10.13 High Sierra and 10.14 Mojave: https://dl.google.com/dl/chrome/mac/legacy10_13/GGRO/googlechrome.dmg
Mac OS X 10.15 Catalina: https://dl.google.com/dl/chrome/mac/legacy10_15/GGRO/googlechrome.dmg