Determining the appropriate source for a speech involves more than just identifying something that is on-topic. It involves a critical analysis encompassing all aspects of the source, its context, and how you plan to use it. This can be overwhelming, so Ask Us if you need help! You can also apply the SIFT strategy, a set of four "moves".
SIFT is a handy acronym that will remind you how to sift through all the information you may find on your topic. It outlines a four-move strategy for which you would:
Stop. Remember your purpose. Ask yourself what you already know about the creator or the source.
Investigate. Know what you're reading about before you read it.
Find. Find coverage or consensus on the primary claim of your source before trusting it.
Trace. Trace information back to the original source to re-contextualize it and gain a better understanding.