Good luck figuring things out! Do let all of us know if and when you get a response, as I can't see a button to get a Steam key on my download page either.
If you keep having problems with itch.io support not getting back to you, I suppose you could get Steam keys directly from Steam and send them by email to all owners of the itch.io game? If that were the case, it'd be also be a good idea to send an email to customeres to ask if they are interested in one and to have them reply with their unique download link to confirm their ownership of the game.