Megamart is in The Center on the road between Ramada Junction and Jaidah flyover. You'll see the KFC in the car park as you drive past.

I almost died during the Marmite crisis of November '06, when Megamart didn't stock it for a few weeks. It even warranted a blog entry; http://tall-and-ginger.blogspot.com/2006/11/good-news-bad-news.html

Oh, and for the record Vegemite tastes like poo-poo compared to Marmite!