Depending on your budget and hunger, sportives are increasingly turning their eye to long distance challenges. There are a handful that go over the Alps, for example, and even one that goes around the world. I've not looked into it, but I'd imagine there are others (trans-Am?) that are long but not bare bones audax rides. After all, you need to start looking after yourself at 50 :p
A more humble challenge, but with some history in Audax UK, is Trafalgar-Trafalgar. I've been intrigued by that ride since I joined AUK a decade ago. Likewise Brindisi-Calais. Both are (or at least were) permanent events.