Microsoft’s own servers (via the Volume Licensing Service Center – VLSC) or a trusted MSDN subscription. However, for single users, Microsoft no longer hosts the retail ISO directly. You must use the official downloader.
Microsoft Office 2013 End Of Life | Next Steps - Woodstock IT Microsoft Office 2013 Standard 32 Bit Download Iso --FULL
If you have a retail product key (common for editions like Home & Business), you can attempt to register and download the installer at setup.office.com LG Networks, Inc. Alternative Official Resources Microsoft’s own servers (via the Volume Licensing Service