There is no standard app store for j2me apps, and nither didexist for any other platform until Apple had invented the iPhone one. Since the Apple app sotre, almost all vendors created one, such as OVI for Nokia, AppWorld for BlackBrry and the Windows Mobile Marketplace. Also Sun came up with the Java Store, but it aimed only at desktop apps at the moment.
Since there was a clear void, many companies have created stores for mobile apps, most of theme support non-j2me apps (Windows Mobile, Symbian, etc.). The two largest ones are Handango and GetJar. Of the new stores, OVI and AppWorld sell j2me apps. Other stores such as PocketGear and MobiHand sell BlackBerry apps as well, but not pure j2me ones.
Given that, it seems that most the applications in the j2me are sold via the operators' portals or stores (like AT&T Media Mall) or pre-installed on the devices themselves. The outcome of this is that it relatively hard to sell j2me app, comparing to the smartphone arena (iPhone, Android, Blackberry, etc.)