The Chase Bar and Bistro in Baldivis have a DJ one Friday a month, usually the first Friday of the month.

The Whistling Kite in Secret Harbour has a disco every Friday, very popular, calling the Under 25s from Mandurah and Rockingham and everywhere in between.
I have only been there once. It's like a night club, except that the queue to get in starts at 8.30 or so! Long bar is a plus for fast service. Dance floor is crowded, no room for partner dancing!

And then there is Encore, above the Vat 116 bar in Railway Terrace, open until 2am. You can catch a band and then there is a DJ from 11.30 or midnight until 2am.
Encore also has RnB disco nights on Thursdays.