We've seen a lot of 05-09 S197's needing alternators lately. Even now that the winter has past and they don't have the to work quite as hard to recharge the battery. I guess it's just that time the factory units start to let go.
Both of these alternators are expected to be back in stock at the end of this month. At the very latest, I'd say the first week of June!
Give me a shout if you need assistance with anything else.