Find NOS or original. I bought a pair of mint ones just last year. Also bought a NOS passenger side a few months back. I have seen several other nice sets for sale since so they are out there.
The other option is to buy the 70-71 reproduction fender and fill the marker light holes. There are no flanges on the cutouts for the 72+ sidemarker lights so its simple to cut the holes for them. An air file is great for getting the square holes perfect.
I can get pics and measurments if you need them.