there are plenty of systems that can provide targeting data from outside the 1000km envilope. AEW&C, SBIRS, OHR, SSK/SSN to name a few.
That list is really pushing it. In real world conditions most of those would be not very reliant, and good deal of them would usually not be available at the needed time and needed place.
Submarines would first need to be at the right spot at the right time - which in itself is not an easy task, especially for SSKs. Then they'd need to be very close to surface, if not at periscope depth to trasmit data - all of which would greatly endanger them.
Over the horizon radars would have an extremely hard time distinguishing what they're seeing, definitely not enough for targeting. Besides, only a portion of the seas is covered with them and only a few countries use them - not applicable for all the jassm users.
SBIRS, as it stands today, is A) not meant to be used for naval ship identification (even if a satellite detects something - how will it know which what sort of ship and whose ship that is?) and B) even in perfect conditions, there arent enough of them to go around detecting ships. Those sats still be detecting such small IR signatures on a wide area - they'd need to be fairly overhead. It's highly unlikely they could be relied upon for regular targeting info.
AWACS and any other airborne radar platform would need to be at some 400-450 or so km away from the target, probably a bit less if we want positive ID. So it is again a moot point to fire a missile a 1000 kms away from a plane A, when plane B can't be more than 400 kms away.
Once again, a NSM with its LO features and IIR seeker is more than enough for most missions. If you've got to fight through enemy fighter cover to get within launching range - that means they're either got an aircraft carrier (in which case you've got bigger problems to worry about than a ship with PAAMS) or you've pinned them down, fairly close to their coastline and they're using their air force to protect their ships - in which case their navy is already half neutralized anyway. Either way, throwing fighter cover in this equation changes everything, as it's silly to even think of engaging the ships themselves without taking care of their air cover.