Maybe try GoHastings.com?
I would look myself, but the full site is way too big for the iPhone.
The mobile site is not very helpful.
I tried DeepDiscount, they just have 1,3,&4.
eBay also has a crappy mobile site. (kept giving Flags of our Fathers)
Nothing on Half Price Books Marketplace (similar to Amazon)
Amazon has 1,3,&4. They used to have the Anime Legends version (which had all 4 discs) but they no longer carry it.