I'm going to assume you've deleted or over-wrote the one that you had. No problem. I, personally, don't know of a place that has one for download, but you can get another one easily enough. Rename your existing 1.0.7.0 WorldEd in some way to keep it safe. Then run the Arcanum 1.0.7.4 patch again. That'll create a new WorldEd for you.