In my most recent Republicans implode TL, I added 11 Democratic Senators. I figure that there would have been enough to pass the background check bill.
I assume that Democrats from Arizona and Nevada vote yes. They are not up for reelection until 2018. While the guy who beat Mitch McConnell would probably vote no, red state 2014 reelection, the guy beat Rand Paul who doesn't go before the voters until 2016, votes yes. The guy who beat Mark Kirk votes yes as does the guy who beat Arlen Specter in 2004 and won reelection in 2010. Since he replaced the co sponsor of the bill,he is a wash. Senator Norton and the other Washington DC Senators support the bill. I don't know much about the gun culture in Puerto Rico, so I assumed those two Senators vote yes. That makes the score 62 yes and 46 no. That is just the enough to break a filibuster in a 104 member senate.