Just go pretend your deer hunting. Then they will come out in the hundreds. that's what happens to me anyway during deer season.
Try sitting and scraping 2 quarters together. It mimicks the sound of teeth scraping acorns and nuts. They always seem to come to see who is making the noise.
i always used dimes. the pitch is a little different, sounds closer to the sounds the squirrels make when they're popping nuts open, to me at least.
another thing, if you lose one going behind some leaves in a tree, i've quickly raked my hand through leaves then went right back to motionless to bust them. that will usually make them start barking, and when they bark, they almost always twitch their tail. easy pick, at that point.
My advise is to wait till late in the year. Sure is is fine to hunt them now
but prime time is true fall. All above advise is valid.