There are many ways that you can buy a CD or digital audio file. But I prefer these channel following;
1) Amazon Japan; Recently, Amazon Japan delivers some stuffs from Japan to some countries now. CDJapan is good choice too.
2) If you would like to buy digital version, itunes is good choice. If you want hi-resolution file or MP3, I recommend you, Mora. Anyways, you have some tricks to buy from that channel.