J-list has a small selection of eroge. You can also try AmiAmi if you are looking to preorder a upcoming eroge. You can also try mandarake or use a shopping service.
Well, not that the "not to be sold outside japan" thing works much anyway (hint: for starters, most those english-reading immigration checkers can't read JPN+they skip over the small-worded notice too haha)
Hasn't stopped me from importing any JPN stuff.
Of course you could always buy the eroge digitally online through MangaGamer or dmm.com