I ordered mine from Seiya. On Rakuten they're pretty much gone (last I checked there was just one seller offering a green), but but you can find them on evilBay for up to 10% more then Rakuten. I didn't look, but they're probably also available on Yahoo Japan. As expected, this first batch was going to go pretty fast, but I bet that in one or two months they will be easily available.
And yes, Casio definitively is going to release different versions - this one will be a fat cash cow for them.