Other than checking with Evenflo, I'd suggest you keep an eye open on Craigslist for someone selling a used Discovery 5 with a cover you like. Recycle the car seat, and put the cover on your known-history seat instead. While I would never recommend a used car seat from a stranger, the cover off a used car seat should be fine.
Also, before you use the seat, I would recommend you go through this check list to make sure it's safe to use, or to put it back into safe condition. After that, take it to a car seat clinic or CPST for an inspection in case there's anything you missed and to make sure you know how to use it correctly. One thing I find a LOT at clinics when people bring hand-me-down car seats is that the seats may have been reassembled or adjusted back to the newborn settings incorrectly. This is usually something we can fix (especially if you bring the manual with you).