Hello, well there's no easy and standard way to do that unfortunately but here are a couple options:

1. In some cases, you can create a check in updown targeting the status page of the third party, and with a little hack: using the contains feature with a string like "All Systems Operational" you can make the updown check detect when the third party is all good. It'll be considered as down in all other cases though, but that could be an easy way. Also if you do that, you can include the URL of the original status page in your Alias, or in your status page description, or simply let the URL visible with no alias, so that your users can go check the original status page from the third party for details about the outage.

2. You can write your own status page in HTML + JS, by using the updown.io API directly to fetch information about your checks, and other API from your third parties to get their status. This is obviously more work but can also lead to a very customized status page with all the details your need (and can get from the APIs).

3. Much more simply your can specity the links to your third party status pages in your description, just so people can easily check them in case there's a problem which is not visible on your own status page.