The Crysis3 Community Group |C3CG| Steam still has keys available to it's members. It's public group so anyone can join.
If you're not a member, visit the group's site (while signed into Steam) and Join the group. Then send me a PM here. Please be sure to include the user name you used to join the group and I will send you a key to the Alpha.
Available on a first-come-basis

Note: if the site says it's private and that you must be invited, that means you're not signed in to Steam. The group is a public group