Where can I find photos of the same place in all four seasons?

I did an advanced search on Flickr for "four seasons" -hotel within Creative Commons-licensed photos that allow commercial use and modification. There were a few good results. You may want to try searching for different keywords.
All of the default Fluther avatars came via this method.

I would also recommend searching various engines with "extended time lapse photography".

Or you can find a photographer in the location you're looking for -- e.g., find a nature photographer in Colorado (which has really strong seasons), and find out if s/he has done a series.

Or, similarly, look around on Flickr for someone (creative commons or not) who has the look you're going for, and see if they have something available (since it sounds like you're looking short term, rather than being able to wait a year for the precise result you're looking for)

Few examples:
http://www.flickr.com/photos/storm-crypt/sets/72157600074678667/
http://www.flickr.com/photos/storm-crypt/sets/72157600074678409/
http://www.luckyoliver.com/photo/2948022/the_four_seasons_of_the_oak_tree

Good advice, alabare. There are some great results on Flickr for "time lapse" seasons -hotel, but presently none of them are licensed under the Creative Commons.

you could also try searching for images of a landmark, it probably wont return the same viewpoint/angle, but it'd be the same location.

Web camera (web-cam) archives – there are heaps of these on the Internet.

Several doctors in my city have pics like these hanging in their offices. They are amatuer/semi pro photographers and have all taken series of pics like these. Look for photographers in your area. There are some really good ones who aren’t professional and will sell you their work for a reasonable price. Any professional who does any nature or landscapes will probably have a series available.