Back in 2015, Apple set up an official "Made for Apple Watch" program for third party watchbands. It can be found here: https://developer.apple.com/watch/bands/
The official watchband lugs to use for making such certified bands are offered through an authorized distributor: https://mfi.avnet.com/lug/index.html#/home
However, 2 years later I still cannot find any third party watchbands that are "Made for Apple Watch" certified, even though there are lots of third party watchbands and even companies solely dedicated to Apple Watch bands.
The official watchband lugs to use for making such certified bands are offered through an authorized distributor: https://mfi.avnet.com/lug/index.html#/home
However, 2 years later I still cannot find any third party watchbands that are "Made for Apple Watch" certified, even though there are lots of third party watchbands and even companies solely dedicated to Apple Watch bands.