Good luck! I've been working the swap meets and ebay for a few years now trying to assemble a good set of the Signal Stats and the plastic lenses are find to find by themselves. Saw a few sets of nice, complete lights (the fronts) at Macungie for $100/pr
As I have not found anybody with NOS or replacement lenses, you will probably have to resort to doing what I have done and that's to start collecting lights until you have enough salvageable pieces to put together a complete light set (I'm outfitting two trucks, so my shop is starting to look like a light shop ...).
Just make sure you know which model light set you have (or want) as even among the Signal Stats, they vary and the arrows aren't all the same.
And there's more makers than just Signal Stat (and they all look sortta alike until you develop an eye for them).
It's kinda fun going for these lights... There's more I could tell ... maybe after I've gotten mine
John