Нужно получить доступ к IMap:
Dim pDoc As IMxDocument
Dim pPageLayout As IPageLayout
Dim pGraphContainer As IGraphicsContainer
Dim pMyMap as Imap
Set pDoc = ThisDocument
Set pPageLayout = pDoc.PageLayout
Set pGraphContainer = pPageLayout
Dim pElement As IElement
pGraphContainer.Reset
Set pElement = pGraphContainer.Next
While Not pElement Is Nothing
If TypeOf pElement Is IMapFrame Then
Dim pMapFrame As IMapFrame
Set pMapFrame = pElement
Set pMyMap = pMapFrame.Map
End If
Set pElement = pGraphContainer.Next
Wend