If your targets have different IP addresses, you can use netstat, and grep for port 3260 (iscsi).
$ netstat -nap | grep 3260
(Not all processes could be identified, non-owned process info
will not be shown, you would have to be root to see it all.)
tcp 0 0 172.16.10.16:48471 172.16.10.201:3260 ESTABLISHED -
Then use tcpkill on the local port and destination IP:
$ sudo tcpkill -9 -i eth1 "port 48471 and host 172.16.10.201"
If your targets don't have different IP addresses, it looks like the best way is to increase the logging level of iscsid to 2 so that you can see this message that's logged when it makes a connection.
log_debug(1, "connected local port %s to %s:%s",
lserv, conn->host, serv);
There doesn't appear to be another way to get the initiator-side port out of iscsid.