Hi Marcia,
If the user is quarantined based off that registry key, typically downloads for remediation are hosted by the vendor (such as Microsoft or Apple for example) or on an internal web server. You can place a link on your Remediation page for downloading the file. You could probably host this download file on the NAC appliance but we do not support doing this nor is it documented.
Regards,
Scott Keene
NMS/NAC Support