Perhaps unsurprisingly so, the upcoming HTC Butterfly 3 is said to be exclusive to the Asian markets. This information comes from the upleaks Twitter account.

BUTTERFLY3(B3) will be exclusive to Asian markets. — @upleaks (@upleaks) March 30, 2015

The Butterfly series has mostly been intended for the Asian markets, with both the previous phones launching in Asia first and then had a limited release elsewhere. The Butterfly 3, too, is said to launch in Japan first but will then likely be available in some other markets, such as India. If you're outside Asia, however, you likely won't see that phone in official form but HTC might have some similar variant for you.