Might have luck at a Auto parts store or Camping World or rv parts store should have it. Main thing to do is take a good one with you as there are different sizes that all look alike. Easy to buy the wrong one. Don't ask how I know.
2002 42' Monaco Signature Triple Crown tow 2014 F-150
2014 Voltage V3605 Sold 5/3/17
2012 F-350 6.7l CC 4X4, Sold 10/10/17
The step lights are the same size covers as the top front cap marker lights. you can use it as an example for the store. I found it at a CalRanch store.
This is one of the side ones. I'll try CW this weekend. Or one of the dealers. I noticed other trailers in my storage with the exact same type of cover so I imagine I could get one easily. Oddly enough the Voltage dealer closest to me does not sell parts.
2013 Voltage 3200
2014 Ford F350 DRW