Seems like they made a very limited number of copies.
Edit: Tower says it's unavailable. I don't think it was ever in-stock on Amazon. But some people were definitely able to get it:
https://twitter.com/hana_fumi/status/874249509865259009
Tower's Yahoo shop says it's in-stock, but it might be inaccurate. You could try using a proxy service like Buyee:
https://buyee.jp/item/yahoo/shopping/tower_4542031