Their is one that is place in front of the scope
that works well, their is also another scope that is dedicated night vision.

The second one is used a lot in the UK and is very good but I jsut can't remember the model.

it is also sold here in Aus.

Will try to remember / look up what it is.

Edit
It's sold by Extravision Australia

It is made by Yukon but can't see it on their web site.

Extravision Australia
www.extravision.com.au/