From what I understand (from when I asked a few months ago) CF10 is no longer available. If you purchase CF2016 through volume licensing you can downgrade to CF10, but only if purchased through volume licensing.
You can purchase the lastest and then contact an Adobe rep and downgrade your license but I would recommend upgrading though. We upgraded from CF9 to CF11 and now CF-2016 with only a single minor tweak. CF11 and 2016 are faster and more secure than their predecessors and the latter should be enough reason to justify the upgrade.