I just went out and looked at my taillights. There is a TYC number on the lens. If you don't have that side lens (maybe damaged/broken?) use the other side number.
Just type that number on "Google" and the vehicle it comes from will be shown, along with a source to buy it from.
They will also come up as a L/R pair.
I've done this also on my headlight units and replaced both of them. They look great now.
My 4 unit, headlight set, cost a total of $89 shipped to me and that included new headlight bulbs.
2002 Newmar Mountain Aire, 37', 3778, W-22, 8.1 Vortac, Ultra Power upgrade, CAI (cold air intake), Taylor wires, colder plugs, Koni shocks.