Yes, you can buy the Tektro HD-E710 from Empoweredcycles https://www.empoweredcycles.com/collect ... 203mm-rear
I installed them on our EPino Tandem and we almost double our braking power. Disc are 2mm thick, Pads are longer, Dual piston. Just ask Matt Hughes if he can get you the HD-E525?
EMPowered Cycles (FAO Paul)
20077 Redwood Rd #4
Castro Valley, California 94546
Telephone Number: 510-825-4754