Concert Ticket

I am interested in watching Mariah Carey Concert this Oct. Her website indicated that sales will open 23rd.
I was told that tickets can be bought at convenient stores or ticket wibsite. So i checked online. It seems like only the most expensive one is available.
Is it because convenience stores only sell certain tickets or maybe limited number of tickets?
Where else can I buy tickets?
Help. I really want to watch it.

Thanks.

Mariah-Carey concert on 4th October in Makuhari Messe, ticket"S"- 18,000 YEN, "A"- 15,000 YEN, "B"-11,000 YEN and "C"- 9,000 YEN, only "S" is available online. The other tickets are sold out.

On 6th October in Yokohama Arena, ticket"S"- 18,000 YEN, "A"- 15,000 YEN, "B"-11,000 YEN and "C"- 9,000 YEN, only "S" is available online. The other tickets are sold out.

Only the most expensive ones are available because "general sale" begins on August 23rd. They would have had "pre-sale" through ticketing agencies already.

Thank you for the reply everyone. I didnt know there was such thing as Pre-sale. I will keep that in mind next time.

I also want to ask. As I cannot read japanese, my japanese friend book ticket for me and i will get at convenience store and pay it myself.
However, his name will be on it. Will it be a problem?