You can find them on Craigslist using searchtempest to search a large swath of the country and then pay shipping.
FWIW I had a couple Dana externals and they were the least comfortable external I've used. They took a frame begging for a full wrap belt and turned it into a quasi-lumbar pad three piece design. Some guys swear by them but at more than 60 lbs it majorly sucked for me. However, the construction quality was excellent.