I suspect Apple doesn't have a buyback program for AW, other than trading in for a new model. It's worth asking, I suppose. Last winter I bought a new MacBook Air and when I was in the store I mentioned I had an older MacBook at home but it hadn't occurred to me to trade it in (it was probably 10 years old!). The salesperson explained to me for the laptops, you can just walk in the store with an old model and they'll buy it back from you - no new purchase required. I went back a few weeks later and got $100 for my ancient MacBook which is just a drop in the bucket compared to buying a new model, but still $100 more than I ever expected to get for the old machine.
I've heard the trade-in value for AWH is disappointing. When I upgrade to S7 or S8, I'll probably look to sell my S5 on eBay or maybe TRR.
I ordered my watch and a couple of in-season H bands from Apple, because they ship more quickly than Hermes online (my city does not have an Hermes boutique). I stalked the H website for a few months after buying my AWH and they occasionally have older, previous season bands pop up individually. Eventually I ordered 2 bands from Hermes, and it was nice because you get the same quality of packaging as ordering jewelry or other items from the H website, versus the basic packaging you get from Apple.