>>125427700>deserve a large breasted girlfriendYou're saying this as if it's like a salary increase or a promotion.
If you're going to try and get one and only care about her tits, you're very much not "deserving" of anything
You should go at it by treating her like any other woman, as a rule of thumb going at it differently because of bust size will basically get you listed as a creep.
Try to flirt. Don't bring it up unless asked. You'll only get better by trial and error. And don't go around "stepping up" from more average chests to larger ones, if you succeed in getting a busty girlfriend and she find out you treated other women as stepping stones to rise up in cup size, there sa very high chance that she's going to leave you. Unless she's a total weirdo or a vapid bitch, but you know what they say about sticking your dick in crazy.