There are a few tools that you can use to do this.
First, you can try manually, at the end of the clients url (clientsite.com/addithere) add:
- sitemap.html
- sitemap.xml
- sitemap_index.xml
No luck? Doesn’t mean its not there. You can also use automated programs to help find the sitemap for you. So this should prob be first 🙂
*This is the only one i can find at the moment to do this in your browser, I will update this as I find more.