Man!! do you know how old this thread is ???
The files are named with a known scheme, you just need to grab the system date to work out what the file name is going to be and concatenate it together.
Dim oFSO As FileSystemObject
Dim f As File
Dim sSourceFile As String
Dim sysDate As Date
sysDate = now()
sSourceFile = "Source file " & DatePart(DateInterval.Day,sysDate ) & "-" & DatePart(DateInterval.Month, sysDate )
Set oFSO = CreateObject("Scripting.FileSystemObject")
f = oFSO.GetFile(sSourceFile)
'Your file processing code follows ...