End-of-Life (EOL) announcements contain the milestone dates you are probably looking for. Note that the EOL announcement is not issued until Cisco actually decides to initiate their EOL policy for that product, which essentially starts a countdown timer to Last Day of Support. Some people are under the impression that Cisco issues public statements about how long they will support a product into the future in advance of an EOL announcement, but that is not how it works.
EOL Policy: https://www.cisco.com/c/en/us/products/eos-eol-policy.html
EOL Products: https://www.cisco.com/c/en/us/products/eos-eol-listing.html
If you want to find the EOL status of a product, then use a search engine on that product name along with "EOL" and you should be able to find Cisco's EOL announcement with its milestone dates, if an EOL announcement has been issued.
Disclaimer: I am long in CSCO
