a) Link either doesn't exist on main page or isn't immediately apparent enough.
b) Consider this page - http://www.boostclassifieds.com.au. Today is the first time I've seen it - visually it looks horrible and potentially untrustworthy. If I may say so, your site looks freakin' incredible. But on their site, the first thing my eyes land on is a gigantic list of categories. It takes me FIVE seconds to find the link to "turbos and superchargers" and one click later I'm where I want to be, looking at what I want to buy. Which I guarantee I'm doing right now - in fact I've spotted a couple of GT280RS that look pretty good to me.
I had to navigate through so much shit to find the search page and look for turbos on your site that I didn't actually want to bother.