Where can I find the kernel source for EWS? I'd like to try to build the HyperV network drivers but can't find the source anywhere. The License even states the kernel is GPL but doesn't give a location to download it!
Are you looking for EWS, MEG, or MWG source? EWS is a deprecated product, replaced by the other two as separate appliances. MEG and MWG are based on the McAfee Linux OS, the source of each is in very different locations.
From the product downloads page, after entering your grant number, select "Email and Web Security Appliances v5.* Patches, Diagnostics & Documentation". There will be a license agreement to accept, then you will be presented with options for the 5.1, 5.5, and 5.6 source downloads.
Note that any changes you make to the system will not be supportable, and if you need to call support they will probably not be able to work on the system. Also, 5.1 and 5.5 are end of life. Version 7 has source available in a similar way, but the modifications there would also not be supported.