Does anyone know of a keylime filling that does not have to be refrigerated?
No, it's usually curd or egg related. If you want authentic or scratch, there is no option.
You can add Key Lime extract. I get mine from Olive Nation. If you add it to a base recipe that doesn't need refrigeration, that would work. It's hard to get the concentration of flavor from extract only. But a subtle taste could be achieved.
I use condensed milk & lime juice for mine, it can go a while without needing refrigeration and it's delicious, I get compliments on it all the time.