Replacement Kool Stop Ultimate Guide Brake Pads for the Luna X1, X2, Z1, and Apollo (SRAM versions only!).  These are drop-in replacement brake pads and come as a single set.  You will need to order 2 if you plan to replace your front and back. 

How to confirm compatibility prior to ordering: If your bike came with DNM forks or the caliper says Dominion this is incompatible. If the caliper says Guide on it, it is compatible