It sounds like you may be looking for the for FortiClient VPN version 6.4, rather than the online web installer that downloads components during setup.
: Protecting sensitive data from "Man-in-the-Middle" (MITM) attacks. Compliance forticlientvpnonlineinstaller-6.4 offline installer
Download the file labeled FortiClientVPNSetup_6.4.x_x64.exe (this is the full offline installer). Method 3: Third-Party Repositories (Caution Required) It sounds like you may be looking for