While we don't yet have a dedicated case for the NI Maschine Mikro MK3, one of the cases in our UNISON line may be a good fit!
The dimensions we have on hand for the NI Maschine Mikro MK3 are: (12.59 x 6.96 x 1.77) inches. If that aligns with what you have, we would recommend looking at the UNISON Custom Edition: Compact: (16 x 13.7 x 4.7) inches.