The developers are still trying to make the distro exclusively for the 64-bit platform
They are still in the process to remove i386 Ubuntu Server CD image and are focusing on the 64-bit platform. Nonetheless, other supported installations mechanisms for i386, such as mini.iso and netboot are still present and users have access to them.
According to the developers, unlike the desktop flavour, they're trying to fit the 12.10 server image onto a standard CD image (703MB).
Download Ubuntu Server 12.04 Alpha 3 right now from Softpedia. Remember that this is an alpha version and it should NOT be installed on production machines. It is intended for testing purposes only.