Optics Planet offers the Eagle Optics Rainguard for binoculars from Eagle Optics.

Keep those eyepieces dry and clean in any weather. This rainguard is a simple and effective device for protecting your eyepieces from weather and damage to the glass. It easily attaches to your binocular strap so it won't get lost. It is quick to remove for viewing and quick to return to the eyepieces so you won't miss a thing.
Fits most full size and mid size binoculars. Adjustable, easy to attach, strong and durable, and washable surface contaminant.

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Eagle Optics Binocular Rainguard Rating & Reviews