Just did a bit of checking myself and yes, listed at Calumet for delivery right now and at Nova as coming soon but neither mention stocking R3 chemistry nor could I find any reference to a stockist of R3 chemistry using Google. It would seem that Nova's price means that compared to Ilfochrome paper or even Calumets type 35 reversal paper it is practically giving it away. It undercuts Calumet considerably but the whole issue raises more questions than answers.
Incidentally for U.K. lovers of Kodak Ultra Endura and who are prepared to attempt cutting themselves Calumet are prepared to sell a 12.7cm(5 inches)x 176 metre roll for £36.77. If my maths are correct that is about 977 sheets of 5x7 inches so under £4 a box of 100!!
Is this a pricing error, I wonder? It does say to call for availability which indicates it isn't in stock as most of the other stuff is more expensive and available immediately.
It might be like the old joke. Customer goes into a shop and says an item for which the shop is asking £10 is advertised at £5 in the shop opposite. Shopkeeper says: So why haven't you bought it from the shop opposite?
Customer: Because it hasn't got any right now.
Shopkeeper: OK then, when we haven't got any, our price is £5 as well :