The only thing I can think of requires being a bit of a craftsman and artisan.
- Make the female mold
from the good side.
- Make a new Male form for the good side.
- Make profiling templates out of plywood
- these are the same kind of templates used to profile racing
keels - think fancy french curves. How many you need will depend on how much taper and profile change there is couple with your skill as an artisan.
- Blow foam into the good side - If you have access to a packing foam machine that would be ideal - build up the foam enough soe you can cane carve the opposite shape
Then the hard part - carve the opposite shape by hand using the profiling templates to guide the final form.
If you've succeeded this far you now have a male plug
from which to make a female form.
I can't think of an easy way.
If you have access to a CNC shop they may be able to map the good side and then "machine" a wooden mirror male form - Might be expensive but lots of specialty auto and motorcycle shops have CNC machines these days (in the US) maybe not so much in Turkey
- Make two good "left" sides
- section 1 of the left sides laterally into say 1 inch slices
- Flip over and lay these "slices" into suitable base - say heavy sand covered in thick plastic
- You now have a very "Choppy" female mold
for the opposite side
- pour a plaster mold - male
- build up the plaster mold with bondo
- fair, sand and shape using aforementioned profiling templates
- Make another female mold from this from which to make the final fiberglass