Aviation Easement is the way to go. Need at least a 30:1 slope protection from the threshold. That's the magic number for FAA night visual approaches at public airfields (more or less...), but you need it for pretty far out if you're really worried.
Most people will sell their air rights because they either have no idea what it means, they like "free" money, or they just don't have any desire to ever build that high. BUT, most people also don't want an approach over their house, so if they know what/why you're doing it, they'll probably say NIMBY.