I have been looking for a better track screw for a while now but haven't had any luck. Wild Bill's here in MI has a bag of 50 or 100 screws that work well, very close to what Atlas sells with the button head. I can post pics if needed. They are slightly longer than the screws Atlas sells.
I tried some flat head #4 by 3/4" but the heads are too big for the ties so my idea of countersinking them and painting with RR Tie Brown was not going to happen. We have a few specialty fastener shops in the Detroit area but I still haven't had much luck.