I'm not sure that 'equivalent to Game' means the same as 'good', but anyways..

Japan has lots of game stores and they generally have good prices, particularly on second hand titles, (Jet Set Radio Future: 5 quid, FIFA 2002: 2 quid, SSX tricky: 3 quid).
Where abouts in Japan are you going? Osaka and Tokyo both have districts dedicated to electronics, where you'll be seriously spoilt for choice. One large chain of game shops is Softmap, the one near me has 5 or 6 floors each of which is much bigger than your typical high street game in the UK. It has an entire floor for second hand stuff, an RPG floor, even a porn games floor!