Gemini CDM 4000 – looking for case

Best bet with “strange” sized units is either the manufacturer and if they don’t make flightcases, on their forums.

Should both result in no luck, you can always have one custom-made. This can be done online and irl. Prices generally a bit higher than off the shelf products, but you get to have it made to your exact specifications, for example with extra room for cables, a place to hold CDs, pens, paper, whatever.