Hardtec has WebDT 366 Internal Battery (81-215-375070) in stock for $29 US before shipping (looks like USPS Ground for US and USPS Express International Flat Rate ($33.95) for International). They're used, but could be better than nothing.
http://www.hardtecsurplus.com/servlet/the-82/WebDT-366--Internal/Detail
I found this while looking for a source for a dead battery for a WebDT368/Atigo T. Hope it helps someone.