While we don't yet have a dedicated case for the Behringer Vocoder VC340 Authentic Analog Vocoder, one of the cases in our SUSTAIN line may be a good fit!
The dimensions we have on hand for the Behringer Vocoder VC340 Authentic Analog Vocoder are: (25.55 x 10.12 x 4.06) inches. If that aligns with what you have, we would recommend looking at the MOBILE PRODUCER BACKPACK. This has 4 velcro pads that you can adjust to the size of your machine.