Those aren't the slots, that's the I/O section (keyboard, mouse, USB , Ethernet, etc.). ATX motherboards can have multiple layouts for the I/O section, therefore, they require different 'back plates' for use with ATX cases. Your best bet is to search Google for "ATX", and "back plate" in conjunction with your motherboard's make and model. Also try eBay. Typically, back plates cost about $10USD.
Alternatively, if you can't find one that fits your motherboard, you can make your own out of plastic, aluminum or sheet steel.