Different models use different parts, here is a list of brake pad information.
RUSH/CTY models
- The brake pads are Q15TS TRP 4-Piston Sintered Metallic Pads from Tektro / TRP. You can find them via these two links:
MOSH/CTY
- The brake pads are SP10.11 TRP 2-Piston Semi-Metallic Pad from Tektro / TRP: You can find them via these two links:
You can find the best way to replace these here: https://support.serial1.com/hc/en-us/articles/4402034363156
You will also find that these pads are regularly available through most local bike shops and various online retailers.