Ask authors for some data (after already asking one of the three authors without getting an answer)
I would wait longer for a response before following up or contacting the others. (Sticking with the "corresponding author" listed on the paper should be appropriate unless they are currently on leave from their position.) The authors may be busy and may not have gotten around to it. 

The process of answering may also take some time. If you're the first one to request the data, they might even be talking among themselves about who has a clean copy, whether they want to release the data, whether they can release the raw data as well, how to verify you would adequately protect (raw) data, whether they have updated data to share, etc.

In the meantime, I'd suggest digging a bit more into the source of the data (did they do the experiments themselves? did they tediously collect it? did they buy access to the underlying data or get special permission?) so that you can see if you could replicate or approximate it. You could also see if any of the works citing them have used the same data (i.e. if there is evidence they have been willing to share it with others, that would suggest they are more likely to share with you).

You could also scour their academic websites and CVs. 


Is further information available on their websites, like an unpublished appendix? 
Is there a rendering of the graph online that somehow has the key data embedded in it? 
Through their CVs, can you find potential points of contact? (E.g., if an author attended grad school with your advisor, or coauthored with another professor with whom you've taken a class, those profs might be especially good to ask advice of. If the prof you ask is on good terms with you and the author, they may even write an email on your behalf asking about the data.)