Special sites...
I know of no such entity. Are you looking for discounts because you or your child is a cadet? I don't think they exist either.
Rule of thumb: for Parents Weekend (Thurs before Labor Day through Labor Day) BOOK EARLY, whether you fly into COS or Denver. Find the type of accommodations you need/desire and BOOK EARLY. In case you were wondering: BOOK YOUR RESERVATIONS... TODAY.
There are no real financial perks to having a cadet at USAFA as far as the airlines go (or that used to be the case, and I doubt things have changed). But, your firstie, or 2* or even 3* will figure out that they don't need or want Mom & Dad to make their plans, especially for rides back from the airport. Somehow, they just show up in Denver and voila! there are cadets and ADAF people there willing to get them to The Hill on time.