The "SM Bus Controller" is part of the Intel Chipset. Instead of looking for a specific "SM Bus" file, you need the Intel Chipset Device Software.
Occasionally, Windows Update may override or block the driver. : asus h81m cs sm bus controller driver
: ASUS does not list a separate "SM Bus Controller" driver. It is always bundled inside the Intel Chipset Driver package. The "SM Bus Controller" is part of the Intel Chipset