Since you're not making a garment, finding the EXACT same yarn isn't as essential in this case. Make sure your new yarn has these "qualifications":
The label says "Super Bulky"
The label has a #6
The yarn itself is nice and smooth (not one of those furry or fuzzy ones)
Something else that's important is getting the right amount of the equivalent yarn. In your pattern, you need 4 balls of Zoomy, which would be 332 yards altogether. Whatever new yarn you choose, make sure you get at least that much.