I got them through cobraracing on this forum his website is
Cobra Racing

Although one of the other guys at our track just got some protek LiFePO's for his mugan - they are a little bit bigger and just fit into the battery box they also have a bigger capacity

Amain LiFePo

As a comparison cobras LiFe hump packs are dimensioned as followed

1300mAh
51mm L x 31mm W x 24mm H

The Amain ones are as follows:
1700mAh
55mm L x 31mm W x 32mm H

Hope all this helps