Hi,
Thank you for your interest in Syncfusion products.
The QTP addin for 6.4 version will be available in the version history of our website, where you can download the setup and install it in the system the has Essential Studio of version 6.4 and QTP 10.
Please find the version history page from the below location:
http://www.syncfusion.com/downloads/version-historyIf you can't find the requiered version of QTP add-on then please let me know along with the exact version that you needed, so that I can provide you the exact location of the setup.
Let me know if you have any other concern.
Regards,
Nirmal