First of all what is wrong with the current caliper that means it cannot be serviced?
A number of garages resort to part swapping rather than fixing/servicing items - very lazy but allows them to offer an assured service. There isn't a lot to a caliper to go wrong, but can need to cafe manipulation of the cylinder to get it moving again and fit new seals.
You could try another garage or even a Motorcycle centre to have a look. Try and find a brake specialist.
Obviously I don;t know what is wrong with the current caliper.