Japanese power cable for 3-pin power adapter.

Next week I'm moving to Japan, and hope to continue using my laptop there. The power cable is split into two pieces: one piece connects the laptop itself to the AC adapter, which accepts 100-240V, 50-60Hz, which should mean no problem with Japanese electricity. The other part is just a cable that connects the AC adapter to the wall socket. The one I'm currently using has a British wall socket plug, so obviously this will have to be replaced with one that has a Japanese plug. There are plenty of these available, but they all seem to be 2-pin. Now, when I say 2-pin I'm not referring to the wall socket side of things, but to the connection between this cable and the AC adapter. The vast majority of these adapters are indeed 2-pin (looks like an eight or infinity sign), but mine has three - kind of like the 2-pin one but with an extra hole arranged into a triangle formation. Do you think I'll be able to find a Japanese wall socket -> 3-pin AC adapter connector cable somewhere? I would imagine that such a thing should exist, although I guess that if this type of AC adapter doesn't exist in Japan then it might not. I've never tried taking a laptop abroad before so I'm a bit at sea... comments from anyone with experience would be greatly appreciated!