Find the flock feeding - run at them and bust them up. First sneak as close as you can and then run at them.
Try to scatter in all directions. Then pick a place and concetrate on the loners that flew off by clucking and kee-keeing. You will call them back.
Or like above if you find the roost area - sit that late afternoon - they will come back.
Both have worked very well for me
JW