You can search for your required fasteners from the parts library.
From there, you can add them directly to your cart. You can also find them in MachineBuilder, in the Add-ons section, located at the bottom of the parts library tab. The add-ons menu also includes cables, tapping kits, Loctite and other useful items for your assembly. Note that if you add your fasteners from MachineBuilder, you will not see them in the CAD since no fasteners are shown in the design, but they will be added to your BOM.