Now that we know how to use reflection to create these classes, I'm going to suggest that you encapsulate that behavior in a Factory Method so that you can hopefully avoid using reflection at all.

Public Class QuarterFactory
  Public Shared Function GetQuarter(ByVal date as DateTime) As Quarter
    If date.Month < 4 Then
      Return New Q12008()
    ElseIf date.Month < ...
  End Function
End Class

Let me know if that makes more sense in terms of keeping the creation behavior encapsulated in once place (as well as strongly typing it with a date time and a Quarter base class).  Hope it helps,