Hey Simon!
If you want to do a completely 3D printed setup you will have to fiberglass most of the components to strengthen them. There are not to many ready to print .stl flies out there of wings and such (as you have discovered). So you could either use fusion 360 to model up a foil set up, or you could use
https://winghopper.com/ it’s a 3D modeling software made specifically for making hydrofoils (just the wings though). Another option is to buy a clear water hydrofoil setup it will come with a aluminum mast and wood or foam wings, (I think), it’s still DIY but not 3D printed. Me personally I would 3D print the wings and try to make them fit to a prebuilt aluminum mast and fuselage. There are some builds where people have 3D printed their mast but it has some sort of aluminum extrusion or support in it.
Sorry, that’s a lot of info and perspectives. So, if you have questions or comments please feel free to ask, that’s what this forms for!!
Also here is build that might be helpful.