Trident,
Yes, there are strict gun control laws in Korea, but, ironically, there are many gun hunters, while the bow has no such restrictions, but no bowhunters, to speak of. Then, again, there isn't much to hunt in Korea, aside from a few wild boar, deer the size of medium-sized dogs, along with some small game and fowl.
The horn and sinew is another matter. I doubt waterbuffalo would do well in Korea, considering the winters would not be very agreeable. Also, the current cattle situation in Korea makes the situation difficult; for backstrap sinew from domestic oxen, the bowyer needs to get slaughterhouses to specially cut it out in full lengths. It's a difficult and time-consuming process, so most places won't do it; the ones who will charge a premium price for it. You are right that things need to change in Korea to protect two traditional arts: horn bow and bamboo arrow making.