Is there a good way to buy molded LEGO boxes?
I have considered this as well as the boxes look nice and they are stackable. However after taking into consideration how difficult it was going to be to acquire these boxes in sufficient quantity, be able to expand the system as my collection grows, and the fact that even the largest box is quite small, I decided against it. It is just not worth it.

Also, the boxes are not really practical for storage. They are narrow and deep, meaning it is hard to find pieces. I prefer wider and shallower containers where it is easier to see what's inside. It is best to go with a generic storage system readily available at department stores. They are made to be practical for storage, they are cheap, and can be expanded as your collection grows. If you would like to have the LEGO-ish look, you can always paint your shelves in bright colors, add posters, LEGO stickers, etc. 

However if you really-really want these boxes, you might want to team up with eBay or BrickLink sellers who don't really care for the boxes but sell the parts. Try to reach out to larger sellers who buy sets in quantities, so you can get a number of boxes at a time.