It depends on where you are located. But they can be ordered directly from Japan. Shipping from Japan to the U.S. is usually about $35. I have ordered through Rakuten Global. There are different companies that sell through Rakuten. Chuya Online is one that’s good. I don’t see one of those right now, but here’s another.
If there is an Amazon.com site for your country, they should have both of these melodicas.