I can see the product displaying at the cash shop but i can't buy it (have the required royal points)... only reserve it does it mean like out of stock or something? will it be available?
All you have to do is go to the donor section in forums and request there. The name change will take effect in the next server check. While you're at it, you can also request for a donor icon (the gold coin that appears beside user's name on the shoutbox). The request comes free as long as you donate to the server for the first time.
Try list at least 3 names, so they can use the 2nd or 3rd if 1st name is taken Remember to reserve 20 RP in your account when you submit the Change of Name request too
or you could save the ign first on another character and delete it when you know a sc is coming. To test if the ign is taken in the first place you can add the ign as a buddy, if its not taken the buddy request will fail!