Usman, are you saying that Moodle servers have to be internet facing? That sounds crazy! That would imply that you can't run those themes on an intranet. Or at a rural school in a poor country where internet access is not available...
I doubt the founder and creator of Moodle would allow Moodle Themes to go that way, considering that he himself grew up in a small rural settlement in Australia where there was no internet access, so he is quite familiar with the challenges facing poorer schools.
I've run bootstrap themes on my test servers (which aren't internet facing) and they have worked. I've never analyzed the network traffic to see if they do try to access any external CDN's, but it's never been a problem. So, can you explain further why those themes won't work on localhost.
I haven't tested many themes recently, apart form the core themes in Moodle. Are you referring specifically to non-core themes?