I did investigate copyright renewal some time ago for a similar case I wanted to get clearance for at Gutenberg. I remember there were at least two different databases they wanted you to search and it was quite tedious like browsing through tons of scanned images of copyright renewal documents. Unfortunately, there is no single, electronic resource that holds all renewals in a searchable, reliable format.
You simply have to do your best to make sure that you not miss any indication of renewal. This might include even ensuring that the text was not republished (and copyright subsequently renewed) under a different title etc. And the worst of it: even after all this work you cannot be 100% sure that you did not miss anything.
Gutenberg has some relevant information and links to resources:
http://www.gutenberg.org/wiki/Gutenb..._How-To#Rule_6
Jens