I'm sure you have been told but Richard Clark has the only ones I have ever seen and he's not sure if they are any good in the boxes still or not. The material used has an age limit and it has not much to do with UV rays or exposure.
Maybe call him and ask if your search is valid or not. He was going to open a box up last spring for Pete Lockwich who has a 6,000 mile GN and needed fillers. I never heard if he did.