Donald Art Company litho prints are available wherever vintage art prints are sold. You can check online auction sites, classifieds, eshoppes, amazon and more. If you're looking for a specific print you may have to keep an eye on these sites to see what comes up.
Ebay is an especially good place to search, and ebay will send you emails whenever your favorite search items are listed on ebay. Just do a search for your picture... THEN click the link to SAVE that search, and make sure the checkbox for automatic EMAILS is checked. Then you won't miss it when your favorite picture is finally listed!