I may be wrong but a planer blade would likely tear and chunk the rubber if it doesn't try tearing it from the bed.

So I went to the local rubber supply house and compared samples, nothing is a direct match. Closest material is available in the correct thickness but since I needed to machine the grooves I decided to purchase the next thickness up, unfortunately the guy cut my strip from the thinner material and I didn't realize until at home and ready to machine. That said I decided to test a few cuts and see if it would produce the desired look.

(Cut piece held behind original for comparison in each photo)

First pic is simply to see if I could cut the material and if it would be an acceptable look with shallow grooves.

Second pic is an attempt to cut TO the fiber (without cutting into the fiber and weakening, the material only has 2 plys of cloth, so not an exact material match)