I was able to find a yellow lens at my local RV store. There seem to be two major brands of RV lights and it took a little longer to find the type that fit the TM. Good luck looking!
Was the yellow bulb the same size as the one you removed or was it a smaller one? I have found the smaller ones but was unsure if they would work. I guess they do!
I wish I could remember. I would check but my TM is 150 miles away in storage and it looks like we won't be going out for another month. :-[ :-[
My 2002 TM has a bulb that looks like the "Malibu" accent lighting bulbs. I bought an amber one (4 Watt) and it seems to work just fine...
I asked about that yellow lens as they didn't have one on hand when I went back to the RV shop, but the lady looked it up. She said they run either $2.50 - $3.50.