^
http://haropedia.mrwaffle.org/wiki/Concert_GuideI've been to four graduations, and I've always bought my tickets on the secondary market (resellers/auctions). In the past, you could usually get a better deal if you bought a ticket at Gorakudoh in Harajuku once you arrived in Japan, but for Aichan's graduation the better deals were on Yahoo! Auctions Japan.
Since 99.9% of the sellers on YAJ won't deal with foreigners, you'll need to use a proxy service as an intermediary. I've always used Juno at
http://bid-service.jp/ as my proxy for getting tickets on YAJ and he's always delivered the goods.
To give you some idea of the pricing, my ticket for Aichan's graduation was for Arena B-8 block (approximately 25th row on the floor, slightly to the right of the stage). My winning bid was ¥14,200, which came to a total of USD 251 including all postage and proxy fees.