A CL65 ON AN INTL FLT DECLARED AN EMER; DIVERTING TO AN UNPLANNED DEST BECAUSE OF POOR DEST AND ALTERNATE WX.

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AT ETA; XC00; WX CONDITIONS AT THE DEST (ZZZ1) AND ALTERNATE (ZZZ2) WERE DETERIORATING. VIA ACARS; I BEGAN TO DEVELOP AN ALTERNATE PLAN OF ACTION WITH DISPATCH. DISPATCH REPLIED WITH ZZZ3 AS AN ALTERNATE. I CONCURRED. AT ETA; XA45; CTR RPTED INDEFINITE HOLDING INTO ZZZ1. ZZZ2 WAS ALSO BELOW MINIMUMS; 1/8 MI SNOW FREEZING FOG. 6 ATTEMPTS WERE MADE TO CONTACT DISPATCH VIA ACARS; 3 VIA COMRDO. DISPATCH COULD NOT BE CONTACTED TO OBTAIN A LEGAL RELEASE TO ZZZ3; OR TO CONCUR WITH THE DIVERT. DIVERT NOTIFICATIONS WERE SENT VIA ACARS. AT ETA XA30; I DECLARED AN EMER AND DIVERTED TO ZZZ3. ON FINAL APCH DISPATCH DID REPLY; SUGGESTING OTHER ARPTS. I WAS COMMITTED TO A COURSE OF ACTION; HOWEVER. AT ZZZ3; THE ACFT WAS ESCORTED TO A REMOTE RAMP AREA AND CORDONED BY ARPT POLICE. THE FUEL TRUCK ATTACHED. I INSTRUCTED ANY ATTEMPT TO FUEL THE ACFT BE DISCONTINUED; AS THE DOORS WERE CLOSED. ZZZ1 FLT COORD DID OBTAIN PERMISSION FROM UNITED STATES CUSTOMS TO OPEN THE DOOR AND CONDUCT A POSTFLT/PREFLT. MR X ALSO EXPEDITED A RELEASE ZZZ3-ZZZ1. DISPATCH WAS INTERMITTENTLY ACCESSIBLE VIA PHONE. FLT OPS COULD NOT BE REACHED IN ORDER TO OBTAIN RELEASE FOR FLT AFTER DECLARATION OF AN EMER. CONSIDER USING ONLY INTL ARPTS AS ALTERNATES FOR INTL FLTS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT A DISPATCH CTR MASSIVE COMS FAILURE PREVENTED HIM FROM TALKING EITHER VERBALLY OR ELECTRONICALLY WITH HIS DISPATCHER PRIOR TO DIVERTING TO AN UNPLANNED ALTERNATE. HIS DECISION TO DECLARE AN EMER WAS BECAUSE HE WAS OPERATING OUTSIDE OF HIS RELEASE WITH NEITHER THE DEST NOR ALTERNATE AVAILABLE BECAUSE OF WX. THE POLICE ESCORT AT THE DIVERSION ARPT MET THEM AT THE RWY EXIT AND REMAINED WITH THEM UNTIL THEY DEPARTED. BECAUSE THEIR DEP POINT WAS IN CANADA; THEY WERE UNABLE TO CLR CUSTOMS AT THIS DIVERSION STATION AND SO UNTIL A SYMPATHETIC CUSTOMS OFFICER ALLOWED THE ACFT DOOR OPENED FOR A FO'S POSTFLT INSPECTION AND REFUELING; THE ACFT AND CREW WERE TRAPPED.