Custom case builders here operate under the heading "Flight Cases". If I search on this label, I get 4 or 5 makers to contact for a quote. Perth is only a small city, so perhaps a bigger city will have even more case makers.
I have had a case made and I have also had a custom cut on a piece of polystyrene to get a perfect inside for a case for one of my custom ukuleles. Its not cheap. But you can get a simple case or a case with wheels and a strong lock and section for music books and stuff, there is a wide range. If you make a bulk order, you are likely to get a volume discount. They come in plastic or aluminium.
If you want fibreglass resin construction, start out talking to surfboard makers. That is likely to lead you to fibreglass resin construction businesses.