Even doing this yourself....it's going to cost an awful lot, for a very minimal weight saving.

There are videos on youtube about doing the work for either GRP or carbon. As long as the surface is smooth, the release agent should take care of everything else. Although prepping to smooth may mean rubbing the panel down and damaging the paint if it's bad.
Or they get thin sticky film to cover holes that I guess could be used to cover rough or pitted finishes to leave a smooth mould.

Ive toyed with the idea of carbon panels myself, just struggling to justify the amount of cost and work. The majority of the expense seems to be with the moulds themselves. And for some panels like a bonnet or doors, you'll need an inner and outer mould, so 2x the work and materials.

I had a single skin kevlar bonnet made for mine a few years back ( stronger kevlar allowed a single skin, so single mould needed. GRP would have needed inner/outer moulds, so while the base material was cheaper, the cost of two moulds made it far more expensive. )

I saved about 11-12kgs at most. Really not worth it.