You're not fluent, so with your grades, I'd say you may as well not have any language skills at all.
And unless there are smaller/midsized firms that do the type of work you want to do, I'd start broadening your search now. My guess is that the market on business deals with China will be pretty much dominated by the big named firms. You should definitely apply, and try to highlight what language skills you do have and your interests, etc. But you're certainly fighting an uphill battle.
I'd start figuring out what else you might like to do.
On a side note, Abovethelaw has been having pieces on american lawyers in China; maybe you could read through some of those posts and get some ideas on how those people got where they're at (at best, I've skimmed one or two posts, so I really don't know what type of information is in them aside from the title).
Edit: Oh, and mass mailing isn't going to do anything for you (assuming by "mass mailing" you mean just printing out a crap load of resumes and mailmerging a ton of cover letters and mailing). You really need each and every cover letter to be 100% targeted to each and every big/selective firm you apply to. Mail mergers that are impersonal tend to work best when your grades and rank sell yourself just fine by themselves. You need to go the extra mile and sell yourself DESPITE your grades and rank for some of these firms that have extremely high grade/rank standards.