Conrad,
I was looking to buy a set also and contacted Tire rack about 3 weeks ago to see why they weren't available. The guy told me that BFG is changing the rubber compound for a version 2 Rival and that the new ones will be available in the May/June time frame. I ended up buying a set of Dunlop Dirrezza Z2 star specs and so far I love them! You might wanna take a look at them if you can't wait for the new rivals.