FL should have an FX called Fast Dist. There's also Overdrive. Or you could do some research and find a decent VST to download and use in FL. You'd download the file and probably install it to the VSTPlugins folder. Then, when you go to add an FX to a track, click More. Then tell it to search. The new VST should be added to the list of FX. Double-click it and tweak as necessary.