There are small jigs that can be purchased for bending grabs and some even come as a part of better craftsmen kits. However, these aren't generally suitable for making common drop grabs. And speaking as someone who has, on occasion, made his own, unless you intended to outfit dozens and dozens of pieces of rollingstock with grabs, I really don't regard the monetary savings in making your own as honestly worthwhile. It's a lot easier just to reach into the little bag and pull out a readi-formed one that you absolutely know is going to perfectly match the appearance/shape of every other one you attach.
Most hobbyists today are spending $150-$350 per locomotive and $20-$35 per freight car, so how can one seriously quible about the price of a package of grabs?
NYW&B