You more than likely won't need new calipers, just a clean and rebuild should do the trick.
Regarding stainless steal pistons i can recommmend Zeus engineering, they sell a SS piston and seal kit: http://www.zeus.uk.com/land-rover.php
Regarding paddocks i wouldn't bother, they have a habbit of shipping britpart even when you specially ask for not britpart, i've found LR series better to deal with and you're actually given a choice.
HTH,
Jon