Instead, you'll need to spawn it into the game using cheats. Here's how to get a command block in Minecraft, using either Java or Bedrock edition.

While available in Minecraft's Java, Bedrock, and Pocket Editions, Command Blocks aren't readily available through in-game menus. They are unobtainable in Survival Mode through standard play and ...

However, there is a simple trick to spawn the ghastling without the dried ghast block using commands in Minecraft Java Edition.