Has anybody found a "generic" 1/4" x 28tpi machine screw that works as an action screw?

Can get a Fr/Rr set from Boyd's, or singles from Brownells (if ever in stock), but wondering if anybody has found something that works at one of the myriad of online fastener shops out there.

The button head offerings I have found to date have a head diameter closer to 1/2" (.45 or so) and my rough measurement shows action screw head diameter near 3/8".