Originally as pre-order bonuses, the Dawn Till Dusk Keyblade and Phantom Green Keyblade have been listed for individual purchase starting May 8th 2019. Dawn Till Dusk seems to be on both the Xbox Live and Playstation Network stores for Australia at the moment. Both Keyblades are listed for $4.95 AUD each.
While these are only for the Australian stores as of now, it's expected they will be on the rest of the digital stores soon after. As of right now the Midnight Blue Keyblade isn't available on Playstation Network.
We will keep you updated as more information releases for these Keyblades!
UPDATE [May 8, 2019]: The three Keyblades are now available worldwide on both Xbox Live and Playstation Network.