Why does Attic not use "dual"?
 

Do I need to learn the "dual" forms to read the New Testament or Homer?

Duals are pretty rare, but they do show up. Any time I find a form that completely stumps me, it of course ends up being a dual. I wouldn't worry about them too much, but you should at least be familiar enough to know where to look in the grammar book when you can't figure out what the hell that form is.

BTW, I can't really think of a wider difference in ancient Greek between New Testament and Homer. 800+ years. When you get there, you might want to consider picking up a more specific lexicon for either one. I have an old Homeric dictionary that I love (got it at an estate sale). I'm sure there's something more modern out there than my 1904 reprint of Autenrieth.

IIRC you'll see dual forms here and there in Homer (or maybe I'm just remembering older alternate genitive endings), but otherwise, seriously, don't give them a second thought. You won't see them studying the NT.

PS: Homer was a blast to study in Greek, but if you're interested in the NT, you may just want to stick with later Attic stuff. Everything from the diction to the style of Homer is VERY different from NT Greek. Knowing Attic IS a decent bridge between the two, but Homer is far on one side of the bridge while NT is well on the other side.

I haven't seen the one you're referring to, but I own Cunliffe's *Lexicon of the Homeric Dialect* and it is fabulous.