I've had great success cutting my own from a sheet of LEXAN. I've made one a bit taller and wider using the original as a template.
I used a tile scoring knife to slowly scratch through the sheet (flat surface, gloves and patience). I may have been able to use a jigsaw for a faster cut but my finished edge was smooth without any 'waviness' along the outer edge. Minor sanding on the cut edge and good to go.
I replicated the paint along the bottom edge with a plastic paint from Bickel Race Cars Inc (used on polycarb windows) Part#: JBRC4002. Pre-drilled the mounting holes with a new bit. Good off-season project.