For Korean boards your best bet is
Gmarket you will find both Korean and US layout boards their in all kinds of price ranges.
For Japanese boards it really depends on what you are looking for. From what I've seen their is more than one Japanese layout where the only real difference is the size of the space bar and the language keys next to it. That little Topre I have has the small space bar and I'm not really having any issues with it. As to where to get them depends on what you want. So maybe specify if you want a good board or just any old cheap board to play with.
One of the easer places to deal with but with limited choice is
GeekStuff4u the biggest problem with Japanese merchants is that most of them will not ship out side of Japan. So if you really want something very specific you have to go through a buying service. I personally use Crescent-shop they are maybe not the cheapest route (I have not really done a full comparison) but I have had no issues with them so I continue to use them. But the big reason I continue to use them is because they will purchase from any shop in Japan that has a web site and will make purchases for you on Yahoo Japan as well. Another thing is they will consolidate purchases for shipping which helps reduce your costs.
Just be warned none of these options are cheap. All those extra fees really add up. For instance that little Topre listed for around $190 but after fees and shipping it was $275 to get it to my door.
This is getting too long. If you just want something cheap PM me I might be able to help you out. Really do PM me I know of a board I could get you for a reasonable price.