Garmin entered into a similar partnership with Nike on their Forerunner 235 running watch last year. The Nike version had an almost identical similar colored band as the Apple Watch 2. This particular band turned out to be available for sale separate from the watch itself on the Garmin web site as soon as the watch was released for sale.
So hopefully by Christmas it will be available for all.
Nike may be selling the Garmins, but there are no special markings on the watch (like the Nike+ tag on the AWS2) and the color may be similar, but it's not "volt," Nike's special color.
[doublepost=1474312688][/doublepost]PS - they won't be selling official Nike+ bands separately. I don't know what they'd do about replacements, but I assume it's not going to be sold as a standalone like all of the other straps. Note that the Nylon straps that come with the Gold and Rose golf have special hardware that matches the cases, but you can't buy them with [rose] gold hardware from Apple.