Thank you for your response. It seems, that I am not the only one needing this feature. According to those links this feature has been wanted already for years. I really agree with these comments by anim8tr three years ago:
"Hard to believe that Adobe doesn't provide a "Search by Month(s)" feature."
"Right now the only way I can do this is to buy a 3rd Party Plug-in."
The situation seems to be still as primitive as then.