I have been in the same situation as you Dman, and everytime I need a new tire I have to buy two of a new size because I can't find just one. Since I need new tires again soon, I'm switching to Khumos all around because I only average 5-7k miles on my rears, and I need a good performance tire for the rain. Furthermore, it will be a bit more affordable with the Khumos every 3-4 mo's than finding the rare SP8000.
BTW, I'll have two farly low mileage 225/40/17 SP8000's available in a little while after I switch to the Khumos.