I know a few online stores that cater specifically to men:
http://www.rakuten.co.jp/mb/
http://www.b-forza.com/
http://www.rakuten.co.jp/n-select/499233/
I've never actually attempted buying from any of them, because as I've said, their prices aren't exactly that competitive IMO, and I can actually find better selection (and prices) on eBay or even yoox.co.uk. Another problem is that, should you decide to buy something from them, chances are they won't understand a word of English and they expect all correspondence to be carried out in Japanese (since they mainly cater to domestic orders). That would prove enormously difficult for any foreigner not familiar with the language to place an order, especially if they don't take credit cards.
What's the Dior bag like? From my experience their logoed messengers, both new and second-hand ones, are widely available on eBay. Dior does wholesale with their accessories so a good chunk of the stuff you see there is actually authentic. Those from the Dior Homme line are a bit harder to find, though they do pop up once in a while on eBay, such as this one:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...&category=52361