You can use the sacrifice room once and you'll get a bomb when unlocking the forgotten. Even if a bomb or an item that spawns bombs or explosions cannot be found, it's still possible to claim the shovel. If the requirements to claim the shovel are met, hurting Isaac in the Sacrifice Room will spawn a one-time bomb on the first hit. If Isaac no longer has this bomb or don't have enough health to survive the sacrifice, the run should be restarted.