Find the author and ask them for it.
I am trying to download an old version of the dictionary.com iphone app which will run on my old-school iPhone running iOS 2.0. Searched for it on download.com: http://download.cnet.com/1770-20_4-0.html?query=dictionary.com&tag=srch&searchtype=downloads&filterName=platform%3DMobile&filter=platform%3DMobile
Here, it shows results for version 1.0, 2.0, and 2.3. Following the link for version 2.0 and clicking "download now" takes me to an iTunes page to download version 2.3 (which will not work with my current version of iOS). What's up with this? How can I download the old version?