Ordered some Tumbling Dice figures (no pictures) that are in the mail.
Oddzial Osmy (O8) miniatures look good (see pico armor) - see http://www.picoarmor.com/pages/products.php?search=infantry for the variety.
I've got some aircraft from TD and they look a bit different - more bulky - compared to O8. Don't know if that's the case with the infantry.
WW2 Soviet infantry would be my choice for North Korean and Chinese troops - they used the same weaponry, and you can't see the uniforms anyway (though I think they were similar to the Soviet ones).

I'm using O8 infantry (modern sets) and they're great. They come in two types:
- the lying/crouching ones (like the Soviet WW2 infantry) which seem to be more detailed, but also a bit bigger,
- the standing ones (like Soviet modern infantry) - these are smaller.
I like both of these, though I'm not sure if they would mix well in one formation.