I know several on here have bought replacement finder liners or made their own from all sorts of material based on the original sizing.
I thought I would go a step further, as mine were completely gone on both sides, and get them to fit a bit tighter. So I bought some 3/32 rubber sheet and spent the better part of an afternoon slowly trimming cardboard templates to use as a guide for fitment on either side.

The original fasteners were not holding given the thicker material so I opted for short self-tapping sheet metal screws with rubber washers as they grip nicely without twisting the rubber sheet. I also made triple sure where I was driving the screws as there are hard lines and wiring harnesses attached to the inner fenders on both sides.Last I made sure when the suspension is fully compressed nothing rubbed against the sheet either.
In the end they turned out rather well and after hitting a few puddles the engine compartment shows no sign of being wet.

I should note I took this picture today after having installed them late last fall; I'm impressed how well they have held up thus far...

Those look amazing. I hope you don't mind if I totally copy this.

Feel free, it's not like I have time to make them and sell them
Let me know if you'd like a pic of the passenger side as well.