Hey there
There is indeed diving in Korea and what you do I guess is gonna depend on where you are going to be going, any ideas? The best diving in Korea is Jeju island or ulleong do, if your staying on the peninsula then the west sea is extreme low vis, the south has some good sites arounf Goeje and the east sea is generally pretty good offering man made reefs and a few wrecks here n there.
Its pretty cold in comparison to what alot of divers are used to and your job is going to be finding a centre that has western sized equipment for rental. There are a few dive centres in the country that have native English speaking crew - aquatic frontier, deep blue quest in seoul, big blue 33 in Jeju and sea world dive centre (me) in Busan
Diving here can be challenging and although it does not offer the kind of quality of other areas of Asia Pac/SE Asia there is still definately some good dives out n offer and if you have the time while in the country then you should certainly give it a go.
Lemme know where exactly your freinds are and I'll try to be a little more specific
