Start by looking at any numbers/names on the lens and or base. Google those if you already haven't. I know there used to be RV salvage store in and around Elkhart that bought up old unused RV parts. Just in case the light you need has been discontinued. Hopefully the 23 models use the same clearance light making your search much easier. I'm assuming you already contacted the dealers/manufacturers. Good luck.
Do the common uncommonly good.