I'm confused.  Why can't you enter your desired location and dates into the search boxes for Homeaway.com or vrbo.com and see what's available?  Even if you have to repeat it daily, it's really not that onerous to type in a city, state, and two dates. 

Unfortunately for you, most owners work ahead on a much longer time frame than one month.  My guests can cancel up to 2 months ahead with no penalty, no sooner, so the cancellations I post will be posted at least 2 months out.  My guess is you are not going to see many late cancellations for travel in the next month because the original travelers would be stuck with the bill if they cancel so late.  It does happen, but rarely.  You are more likely to pick up new listings as they come on the market instead of cancellations. 

Maybe you could consider traveling to a less popular tourist area where there may be plenty of vacancies even one month out.