I don't believe the cockpit jumpseat is available anywhere anymore is it? But, if your just looking for a ride to San Juan from the mainland you have several options. It looks like your 121, so you take your pick. If you are 135 you can get here on JetBlue from JFK, Spirit from Orlando or FLL, and ATA from Chicago or Orlando. They are all terrific to jump with; thanks by the way.
As far as the Gen Decs. It's US to US (although the PR's may think otherwise), no Gen Dec's required. Hope this helps.