Thanks! I couldn't find a place to drop them an email until you gave me the link - so I do have a question into support now. I did contact their parts supplier, but they don't have them. Could just be the product is too new, and there are no cables available yet...
I had the same question and when I emailed Casio they told me to call this number 1-800-223-2001 to order one.As of this morning, 4/13/16, the cable is back ordered 3 weeks. It cost $20.00 plus $9.00 for shipping. Hope this helps.
Hopefully these come down in price now that someone is making them, but it's already better than what casio wants for $$$. I'll be so happy to have an extra. Smartwatches should ship with two charging cables :\