Pistons usually do not need to be replaced, just be very careful when removing them so you dont put any nicks in them. As you saw, its an expensive mistake to make. I refinished them by plugging all the holes, media blasting and repainting (paint is my preference).
Do not split the halves either. As per Brembo when the caliper is sealed together it 'warps' together. And they will never seal correctly again once split.
I rebuilt 10 calipers about 2 years ago and bought all the seals from here.
Zeckhausen Racing