You can make the grooves for your bands the easiest way with a Dremel and a 3/16" burr bit. Just draw the line you want to cut and follow the line with the burr, shallow at first, then keep cutting round and round until it is almost as deep as you want. Finish the grooves with a 3/16" chain saw file to straighten it all up.
Another way, that I use is to cut the side grooves with a scroll saw while cutting out the fork shape, then use a Dremel to cut the grooves across the front and back. Finish with a file.
Another way is to use a router table and a 3/16" bit with the fence set for the proper distance. You can get three sides with the router, but you will have to do the inside grooves with a Dremel or just a file.
A little short cut with the grooves, as long as it's final look is ok with you, is if you want a groove, with the purpose of extra hold under the tying application is to groove only one side. Both sides if it is a catty that is designed to be flipped around to accomodate the opposite handed person.
I have taken to grooving just the two critical sides and leaving the inside of the forks alone as well as the outsides. I like the look just fine when it is done. One design I only grooved the one side to be under the band due to not affecting the look of the design with a groove.