I don't remember coming across "medias" but I can think of contexts where both "medias" and "mediums" could be used. Mediums: different types of medium, such as floppy disk, cassette, hand signals, etc. Medias: different types of media, such as TV, newspapers, etc, or different TV stations and so on. "Most medias are available on many mediums. TV stations broadcast on the internet and newspapers run their own radio channels." It's ugly but they do or can have distinct meanings.