Your Silver status will get you access to the Greenwich lounge at JFK, and you can guest one of your colleagues.
AA does still sell Admirals Club day passes (they're $79+tax) but following the creation of the joint AA/BA lounges at T8 unfortunately there are no longer any of those left there. As far as I'm aware, the day pass solely grants access to Admirals Club, not any of the Flagship facilities which Chelsea, Soho and Greenwich are.
I don't believe there are any third party lounges within T8, but even if there are you would either need to split your travelling group or spend a lot of money unnecessarily.