Clean install a Macbook without another Mac
This is an interesting situation.  If you have access to an Apple Store, I suspect that going to them would be the easiest way to resolve the problem.  Otherwise, if you have access to a Mac even temporarily, you should be able to sign in on the App Store using your Apple ID, and purchase Mountain Lion that way.  From here, I'm not sure if you'll be able to install Mountain Lion using Internet Recovery, because it is likely for Lion and not Mountain Lion (and I don't know if the Lion Internet Recovery supports Mountain Lion), however, from here, if you download the image, there are various tutorials that you can follow to either burn the installer to a DVD, or copy it to a USB flash drive, for instance: http://lifehacker.com/5928780/how-to-burn-os-x-mountain-lion-to-a-dvd-or-usb-flash-drive

As these are not officially supported solutions, my suggested option would be a visit to an Apple store.