Have been buying from Amore-Venti for a couple of years now. Initially they sold the bags under simplespree blogshop http://simplesprees.blogspot.sg/.
Great buys every time. I get them usually for my wife but shes doesn't know the source of them. The bags came with receipts which made me feel safe.
Can even contact them to pre-order bags if you have a particular design or model you are interested in. They will check with their overseas buyers if they can be purchased. That's great service!
Think the only downside is they do not have a shopfront so you can't really go browse the bags physically. But maybe that's how they kept the prices low.