I’ve got a PXR4 too...
I have a small stereo condenser mic that looks to be a couple of the Panasonic elements in either side of a small tube approx 1” in length with an alligator clip attached and a stereo cable coming out of it. I forgot where I bought it, but I originally used it with a mini disk recorder I had. I think it needs around 1.2V to operate. The mini disk recorder I had supplied this voltage, but I’m not sure about the Korg (probably doesn’t but don’t know for sure since I’ve never tried it with mine…) If not, then you’ll need a way to "charge" the mics if you don’t buy the type with a battery compartment.
They sell mini preamps for this type of thing, but they are $$$.