The only person who can get access to invoices for an account is the account owner. If you are the account owner you can access all your previous inovices from BuzzStream in the Account settings.
First click on the settings icon in the top right hand corner of the app. From the dropdown select Account.
In the "Payment Information" section, your list of invoices is provided in a dropdown menu. Invoices are arranged in order by date, with the most recent invoice at the top.
Once you have selected the invoice click View. The invoice will open in a new window. From here you can use your browser commands to print or save the invoice.