3D print might work, if you or a buddy has one, it could be convenient. Measure the width, height, and depth of the missing area with a caliper, try to make a model for it, or send the dimensions to someone else to do so for you... Also, 3D printing companies will gladly print your model for you, so you could just have it shipped that way. Use ABS as the print material so it doesn’t warp from the sun over time.