Ah, well, let me see if I can help you find them.
Reunion does have the ability to categorize one's sources and when I first imported my GEDCOM into Reunion, I had no such categories-- they were all lumped under "unused" or some such.
Here's how you find them. From the LIST menu, select SOURCES. Make sure TYPE (upper left corner of Source window) is "All types". You should see a long list of all your sources.
Note the options in the lower left corner, specifically "Source Tools". See what you can do there. It's totally cool.
From a particular person's page, you can also see which facts are "sourced" by looking for a red number (or numbers) by each item that is sourced. If you click on that fact (or name), the details for that person come up, and the citations should be listed at the bottom of that window.