What do I do if my world has no corruption or crimson whatsoever? Is there any other way to have meteorite fall?
If your world doesn't have either, someone probably cleansed it all so look for chasms with stone walls. You should be able to find crimson hearts or shadow orbs at the bottom to get a meteor to spawn. If you really can't find anything that even looks like it was corrupted before, you cannot get a meteor to spawn. I would check with a map editor to be sure, though, before generating a new world.
Just to double check, you should download a map editor or viewer like terrafirma to make sure you don't have any corruption or crimson. After you have checked and there has been no sign of the previously stated biomes then you either must look for terrain that looks similar to the biomes and explore there (If lady luck is smiling at you, you will find either a shadow orb or a heart) or make a new world entirely. Sadly, there is no other way to summon a meteorite :(
If your ultimate goal is just to farm the ore, you could import 50 meteorite ore from another world and place it anywhere you like. This will cause Meteor Heads to spawn, which can drop ore. Just make sure it is all kept in the same area (on one screen). You will know you've done it right when the Meteorite Biome music starts to play.
Meteors do not require destroying shadow orbs to spawn. This is just the most efficient method for getting a meteor to spawn. There is a small random chance that every sunset a meteor will come crashing down.