Where to get replacement screens for B&W Nautilus

If you mean grill cloth you can order it bulk from Parts Express and other places and cut it to fit and mount it yourself.

I assume you are in the US and if so, you can contact their distributor which has a parts department. I sourced replacement tweeters from them several years ago and they were extremelty helpful.

B&W Group North America
54 Concord Street, North Reading, MA 01864
Telephone: (978) 664 2870