When they set it to me it was just the two pieces of heavy plastic sheet and a pair of simple “L” shaped brackets. I more or less improvised the installation using some of my own hardware in order to make it stronger. Knowing the size now I’m sure you can find a generic source like from a truck or trailer vendor. Might be hard to cut to size though if it’s made of the same stuff. Good luck.
If you have to replace them do get a thicker poly material that will last and will not flap in the wind. You will need a power tool like a router or jigsaw to cut them.
One side could be different from the other due to where they found the metal to attach them to.