As above, you can do it yourself easily, if you are happy with using GRP.
I did exactly the same with my Mini Marcos a good few few years ago. You make a buck / mold by coating the panel you are copying with release agent then coating with fibreglass and resin (Gelcoat 1st), put a few sections of wood in it on the second or third layer to make it as strong as possible.
Then remove the original panel (that's when you see how good your release agent is!), and use the buck to make your panel. Anything thats wrong with the buck you can fix with normal filler, smooth off and off you go ... I seem to remember some of the 90 degree turns were not perfect when I did the copy, so I just made them good with filler.
I had zero damage to the bonnet I copied - only issue I found was it was such a good copy it copied all the imperfections in the original panel ... hence the filler.
If it's a big or complex structure just put break lines in using cardboard cut to the shape and glass up the sides of these 90 degree returns, drill them so you can bolt it back together when its in bits before removing the bonnet you are copying. If you look at how they build a car or boat with GRP you will see what I mean.
Edited by DomCr250, 08 November 2016 - 09:54 AM.