Recently the Thief and The Cobbler has been showing up on DVD in strange places. One such place is free with a box of Fruit Loops in Canada. You can find some of these for sale on ebay. This is a pan and scan version of the American/Arabian Knights release.
Most recently it was released in the full cinemascope aspect ratio (2.35:1) from Japan. You can order it from CDJapan. Keep in mind that it is region 2 encoded so you will need a DVD Player that will do multiregions or play it on your PC.
You can now also get the Australian (Princess and the Cobbler) release on DVD which is unfortunately pan and scan, but the content is much better (scenes not in the US version and no talking thief). This one is a region 4 disc.
Still hoping for the workprint on DVD someday.