Try the code below:
Public Sub test()
Dim pMxDoc As IMxDocument
Set pMxDoc = ThisDocument
Dim pStyleGallery As IStyleGallery
Set pStyleGallery = pMxDoc.StyleGallery
Dim pEnumStyleGallery As IEnumStyleGalleryItem
Set pEnumStyleGallery = pStyleGallery.Items("Line Symbols", "ESRI.style", "Dashed")
Dim pStyleGalleryItem As IStyleGalleryItem
Set pStyleGalleryItem = pEnumStyleGallery.Next
Do While Not pStyleGalleryItem Is Nothing
MsgBox pStyleGalleryItem.Name
Set pStyleGalleryItem = pEnumStyleGallery.Next
Loop
End Sub
