Shipping is going to kill your wallet if you want a medium-large one. Any fertilizer that is organic will do. A 10-10-10 is easiest to deal with unless you want to get really into it.
Where are you located? Might as well try and get one from a nursery/home improvement store.
Id also suggest LLL Reptile... Dont know the costs of shipping or anything but you dont have to worry about repotting or cleaning since it is already done and ready to be used with your Cham.