I feel confident the following code will do what you want.
Code:
' Find the record that matches the controls.
Dim strFind As String
'-- Use DLookup() to locate the unique [RspnsID] we need
strFind = DLookup("[RspnsID]", "tblSrvRspns", "([SrvID] = " & Me!cboSrvID & ") AND ([URN] = " & Me!cboURN & ")")
'-- Now locate the record
Me.RecordsetClone.FindFirst "[RspnsID] = " & strFind
If Not Me.RecordsetClone.NoMatch Then
Me.Bookmark = Me.RecordsetClone.Bookmark
Else
MsgBox "Could not find!"
End If
It may not be the fastest way, but it will work until we think of a better way.