The best thing to do is go to this page http://www.jazz2online.com/J2Ov2/downloads/ and at the top tell it to filter single player levels, and sort by rating. There's a whole ton of quality stuff.

I also run a blog where I do occasional updates featuring single player levels. A lot of great levels are not featured on it though, so I recommend searching on J2O if you want the widest selection.