The ECS scores are 8.5×11. Any office supply store will have a hundred options for storing documents that size. You don’t need something music-specific.
Orchestral parts are trickier, but architects and engineers routinely use these larger-size documents so there are plenty of boxes made. Again, office supply houses would be a better bet than a music products supplier. Maybe something like this would work. You might have to put many different pieces in the same box, but it sure would be cheaper. It’s not like you have to get at them super-often.