There are a large number of traditional tunes tabbed for ukulele on the net. A great place to start is with the How to Play Ukuleles for Peace ebook. It has traditional tunes from around the world arranged and tabbed by all the biggest ukulele tabbers (including James Hill). Best of all it’s for a good cause. It’s also worth picking up Ken Middleton’s Bluegrass Ukulele ebook.
Here are some others that you can find on the web: