As I note in the introduction to this reading, the only account that we have of Pericles' funeral oration comes to us from Thucydides' History of the Peloponnesian War. The full text of that history is available on line (translated by Richard Crawley) at the MIT Internet Classics Library (a great source for other classic texts).
One section of Thucydides' history that is particularly relevant to our understanding of his views on Athenian democracy and its demise is his historical account of the Mitylenian debate. Like Pericles' funeral oration, this text is a history, but is likely Thucydides' account, shaded by his own interpretation of events, rather than a word for word account of the actual speech made.
Here is an "illustrated" guide to Pericles' funeral oration that provides photos and historical background information helpful to understanding Pericles' speech. The guide was developed by Dr. Janice Siegel.