That's an HD-8 Greenfield - their first model. New parts are not available. Original engines were Fuji (Subaru Robin), or Honda. The Hondas seem to have been better - we're told Greenfield had trouble heeping the Fujis from overheating. You might find this thread useful:
https://www.outdoorking-forum.com.au/forum/u...amp;Main=7439&Number=39215#Post39215