You can make a base for your existing circular saw using 1/4" plywood or Lexan. Remove the saw blade and make the base the same size as the shoe on your saw. Use flat head bolts to attach it to the saw shoe. One hole in the front and one in the back end of your saw's shoe and the new base and 2 bolts are enough. Then mark where the blade guard needs to swing down, remove the base and cut this marked area out. This opening needs to allow the full swing of the guard, but be careful not to remove material forward any more than necessary. Then, with the saw's depth of cut set as high as possible, replace the blade and this shoe on the saw and make a careful plunge cut, lowering the blade slowly down to it's lowest position while it's running This will cut a narrow saw blade slot from the guard clearance hole forward and this narrow slot will act like a zero clearance insert for the saw. I made one of these for the circular saw that I use to break up sheets of cabinet birch plywood outside of my shop before bringing the pieces inside (small crowded shop). I never worry about chipping anymore. It has worked fine for about 20 years now.
Charley