I bought stainless caliper pistons from here.
http://www.etypeparts.com/pages/about-us
They also sell the seal kits. They also plated the calipers and supplied the brake lines and fittings.
Try talking to John he was very helpful to me.
He might have a magic way of removing the stuck pistons.
If the pistons are not fully pushed into the calipers you might be able to push one in at a time with plenty of PB Blaster or you favorite penetrating oil. Use compressed air to push it back out again and gradually see if comes loose.
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