There is no dedicated software released and it will also not be released for the Alpha version. You need to run a server with the -server command. I doubt right now any company will run Arma 3 dedi's based on the alpha.
Of course you can always rent your own dedi and make it a game server but that might not be what you want.
Here is a tutorial how to set up an Arma 3 alpha dedicated server:
- Tutorial: How to run ArmA3 -server on a dedicated server