I can't help on a specific external windscreen, but we have several of these mics at work, and due to their age, the internal foam under the metal mesh had all rotted into dust. This foam cradles the dual element and fills the space under the mesh. I bought a generic foam windscreen from Windtech and fashioned a replacement with scissors.
That might be your problem, but Windtech likely makes something big enough to fit the 825 - maybe the SM58 foam, or RE20 size, if AT doesn't make the original any more.