Last year I used
http://www.cadregister.com/ and searched for "sprocket" then you'll see Madison sprocket in the list, then I used type A plate, 3/8 pitch. Then pick the tooth quantity you need from their list and download the CAD file. This file will only have 1 tooth showing so you need to array that tooth around the number of teeth you picked, they should all match perfectly. We had these
patterns blown out by waterjet, and then had to bevel the outside edges of the teeth to get them to fit in the chain right. If you just stick the sprocket in the chain without the beveling you'll find the chain will only mesh with 1/2 the teeth then ride out on top of the rest. So that last step is important.
I also made a point to make a variety of sizes in the event I needed to change any ratios after the fact.