Oh, they're not commercially available. My dad negotiated with an optical filter manufacturing company to make prototypes because I was interested in commercial

Oh, they're not commercially available. My dad negotiated with an optical filter manufacturing company to make prototypes because I was interested in commercializing the idea. If you were going to do something similar today, very likely your best bet would be to get one side as EnChroma and the other as a neutral density filter (or a tint matching the EnChroma).