NHT Longevity
My first modern (though they're hardly modern any more) audio gear purchase was a pair of NHT 1.3As. I bought them 18 years ago. They're still going strong, though when I bought my B&Ws, they were relegated to the surround channels. Still sound great, though.
As for replacement parts, I just saw that someone's still selling foam surrounds for a pair of Marantz speakers I bought in 1979, so I'm guessing that if you look hard enough, you'll be able to find parts.
I just doubt that you'll need any.