Almost any garden tractor battery that will physically fit will do. CCA isn't generally quoted for mower batteries - it's not relevant. ANY lead acid battery will supply enough starting current to start a 12.5HP in a good state of tune.
If you say what terminal type you need, what side the + termnal needs to be, and what physical size it needs to be, I'll give you a competitive quote for a battery.
phil_saunders(a)bigfoot.com
Phil Saunders
May 2009