Short of having access to a laser cutter/CNC machine to make your own, there aren't really alternatives that accomplish what an ellipse guide does in terms of traditional media. While you can certainly tackle the last two sections of the course without an ellipse guide, the important thing to remember is that freehanding ellipses is still the sort of thing that will require a lot further training/practice as you move forwards.

We want to avoid having students use this last challenge and lesson as an opportunity to further practice their ellipses, because it simply distracts from the core focus of the exercises at this point. That doesn't mean you can't give it a shot, but that it's critical you understand that students are not expected to be able to whip off perfect ellipses as needed, and that it will interfere with how the constructions are built up.

If you don't mind my asking, in which country do you reside?