FLC OF AN ACR B727 HAD NMAC WITH AN UNKNOWN ACFT CLBING THROUGH THEIR FLT PATH. THE OTHER ACFT WAS SPOTTED AFTER RESPONSE TO A TCASII RA. ATC HAD ALSO ISSUED AN ADVISORY OF THE TFC SQUAWKING VFR PRIOR TO THE ALERT WARNING.

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ZNY GAVE US (ACR X) A FREQ CHANGE TO CONTACT MCGUIRE APCH CTL. WE LEVELED AT 7000 FT MSL; 250 KTS; ON A DIRECT COURSE (GPS NAV) FROM CHAMP INTXN TO ROBBINSVILLE VOR. WE WERE APPROX 25 NM SE OF RBV VOR XING THE COASTLINE. INCLUDED IN THE FREQ CHANGE XMISSION WAS VFR TFC AT 10 O'CLOCK POS. WE OBSERVED THE TFC ON TCASII AT 5800 FT MSL IN A SLOW CLB. I MISSED THE CORRECT FREQ FOR MCGUIRE APCH AND HAD TO RETURN TO ZNY TO GET THE PROPER FREQ. DURING THIS TIME DELAY; WE CONTINUED TO MONITOR THE VFR TFC ON TCASII (NOT VISUAL) CONTINUING A SLOW CLB AND MOVING TO OUR 12 O'CLOCK POS. AT THE TIME I MADE CONTACT WITH MCGUIRE APCH CTL; WE RECEIVED A RESOLUTION ALERT. WE CLBED TO 7500 FT MSL. IN THE CLB WE FINALLY OBSERVED THE VFR TFC VISUALLY. I RPTED THE RA AND EVASIVE ACTION TO MCGUIRE APCH. MCGUIRE APCH SAID THE VFR ACFT WAS SQUAWKING 1200 WITH ALT RPTING BUT WAS NOT COMMUNICATING WITH ANY ADVISORY SVC. THIS EVASIVE ACTION COULD HAVE BEEN AVOIDED IF I HAD NOT MISSED THE FREQ ISSUED TO US (ACR X) FOR MCGUIRE APCH OR IF THE VFR TFC HAD BEEN COMMUNICATING WITH AN ADVISORY SVC.