I did a diy cast of my ear canal using diy silicone… Which I fo not recommend, but look for sugru. It’s silicone type I mixed with talcum powder to expose the water trapped in talcum to the silicone over a large volume in a controlled way… Then I scanned the casts and I used a DSLR to take photos of the parts at various angles and used an open source app to get 3D models from the images. Then I used freecad to cut the models with areas to mount the tiny speakers and such. Finally printed them in SLA resin. I made earplugs, IEMS and headphone adapters using the same geometry. They are very comfortable. The plugs are great for swimming.