Because more aftermarket HU use brackets the same way, the chances of removing the clarion HU and replacing it with an Alpine should be no problem. try to salvage the 2 din bracket you original have. When inspecting the original 2 din bracket, you'll notice how it's holding the clarion HU in place. Simply lift the tabs holding it and slide it out. Get the alpine and slide it in. Put everything back in and u're set.

I notice that you're in Korea, butof course you wouldn't have a Circuit City of anything there. But just in case you can salvage the original 2 din bracket, go to a audio store, ask them for it.