If you are not sure if you ran the HALion Symphonic Orchestra installer, please check the following location on your hard drive:
/Library/Application Support/Steinberg/Content/HALion/VST Sound/VST Sound - HSO
If the installer ran properly you shall find in there the item FCP_SMT_001_HSO_Bass_Clarinet_Solo.vstsound, plus 25 similar items for other instruments.