The two numbers are completely un-related. I think you may have misunderstood Vmca.
Vmca relates to the directional control you have on one engine. I'm sure someone with a better memory, or the time to look it up, will give you the exact numbers, but Vmca is basically the speed at which, with one engine inoperative and the other at full power, you have at least a certain pre-defined amount of roll and yaw capability. It is not connected to the stalling speed in any way.
I'm not aware of any aircraft where Vmca is lower than Vs, although someone might be able to correct me on this one. I would imagine that, if you were to find or build such an aircraft, it would either be very underpowered (lower power means lower yaw from the working engine, so more controlability) or have very badly designed wings (resulting in a high Vs).
Hope that helps,
FFF
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