There's Mini STX cases, eg https://www.amazon.com/dp/B01LY4RTMH/?tag=theminutiae-20
Unless you're using a DC mobo, I think https://www.newegg.com/Product/Product.aspx?Item=N82E16811129080 is probably the closest mini-itx case to the deskmini... it's a few inches bigger iirc.