You don't need cPanel for creating VPS servers, you need a Dedicated Server and software, and it's not cPanel, it Virtualization software, cPanel is for Web Hosting, not for VPS servers, only what you can do with cpanel on vps, is to install cPanel on that VPS.
http://solusvm.com/
Buy licese and install it, that's currently the best virtulization software.
You can connect it to WHMCS via plugin, so you can create,suspend, edit and etc... VPS from WHMCS directly and automaticly, and client can manage his VPS.
There are and free virtualization software, like HyperVM
http://www.lxcenter.org/software/hypervm/
But I strongly recommended to you SolusVM
Sorry for my bad english.