When your at the hardware store they'll have those little drawers with all different types of set screws and dowel pins and you name it Clips they'll be in there. If they only have 3/16 Square stock you can you can grind it on your grinder into a half moon. Best thing to do is hold them with a pair of vice grips and repeatedly dip it in water so you're not turning it blue and taking any type of hardening that might be into in it out. That keyway is not under horrible loads for example like a lawn mower key way. The load on that pump is constant load. What I'm saying is is there's not a shock load to be concerned with. I'm pretty excited for you as I think you'll be very happy with your motor... they're wonderful engines