In Minecraft, you can find blazes in the Nether. Blazes are created from a blaze spawner in the Nether fortress. If you are having trouble finding a blaze, you can also summon a blaze using a cheat or you can use a spawn egg.
While Nether Fortresses can be found scattered across the Nether in Minecraft, their spawning isn't entirely random. Nether Fortresses are more likely to spawn on the positive side of the X-axis, therefore moving north or south while keeping the X-axis positive is the best way to search for them.