I don't have much information on S-Korean grenades.
If anyone has information about grenades used by the South Korean forces, mail me.

Fragmentation grenade A-3.
Photo on the right © Ordata (friction fuze)

This grenade is in form similar to the US Mk2A1. Body length is 82mm.
Below you can see the A-3 (left) compared to the Mk2A1. Right photo shows the base of the A-3.
It is unknown if the grenade was actually issued with the M204A2 fuze. The paint is very dark green. The base is lightly stamped with a five point star, otherwise there are no markings.
Photos © Rob V.

See also the A3 shown on the North Korean page, with the photos provided by Cory.
That one is slightly different with different threads.
North- or South Korea?

KMK 1-B.

Who has info?

K-M8 Smoke HC

KE 180 Stun grenade

Hanwah K-400 Fragmentation grenade

Based on the US M67 .
Steel body, internally fragmented (1300 fragments).
The grenade is produced by Korea Explosives Co.Ltd, Seoel.

Height : 90mm , Diameter : 60mm
Weight : 405gram including 130gram Comp. B
Fuze : K402 with a delay of 4-5seconds.
Lethal circle : 15 m

Koryo K-410 Practice grenade

Hanwah K-413 Fragmentation grenade.

CNO/Tech K-416 Practice grenade

CNO/Tech K-417 Practice grenade

CNO/Tech K-418 Practice grenade

Koryo K-479 Drill grenade