Give up the 410 route...it doesn't work...even in Lisp.
I would suggest looping each layout's entities, that way if you come across your block you immediately know which layout it is on...or...create a filtered selection set for blocks, loop the selset and check the owner of the block reference, that way you can determine if it belongs to layout.
Here's another. You can reduce the number of places to look in your selection set by looking only at paperspace.
Here's an example:
Public Sub GrabPaperBlkRefs()
Dim iDxfCode(0 To 2) As Integer
Dim vDxfCodeVals(0 To 2) As Variant
Dim pSelSet As AcadSelectionSet
iDxfCode(0) = 0: vDxfCodeVals(0) = "INSERT"
iDxfCode(1) = 2: vDxfCodeVals(1) = "YourBlockNameGoesHere"
iDxfCode(2) = 67: vDxfCodeVals(2) = 1 ' Paperspace
Set pSelSet = ThisDrawing.PickfirstSelectionSet
pSelSet.Select acSelectionSetAll, , , iDxfCode, vDxfCodeVals
MsgBox "Block references found: " & pSelSet.Count, vbInformation, "Block Reference Count"
End Sub
Cheers,
Glenn.