Deploying more than 2 VM with extra license on 2012 R2 STD Hyper-V

Hi Team,

We have one Hyper-V running on 2012 R2 STD edition and already two windows guests are installed on it. Now the requirement is to deploy one more additional VM on the same Hyper-V. I understand, by default, we can install two windows VM as bundled with Hyper-V std licensing but is their any provision, where we can buy separate license for third windows guest VM on 2012 R2 STD Hyper-V ?

Thanks,