You can get inexpensive custom molding kits to make your own from places like Amazon and eBay. I've tried them and they work well, but I find that the disposable expanding foam type is more comfortable inside a helmet that pushes my ears around a bit.
This is an example. I bought mine years ago and don't remember where I got them.
https://www.amazon.com/Radians-Custo...1038064&sr=8-5