Go to an industrial supply store. Acklands Grainger, Fastenal, Bolt Supply House, Blackfoot Industrial. Check out machine shops. Ordering from online, and from the USA no less, is an absolutely ridiculous idea for a screw that you can buy for less than a buck. Places like Blackfoot Industrial sell them individually, and a pack of set screws is probably $5 for 100. Do the math on that and figure out what one costs.