Interestingly enough, the company that made them is still in business - but they stopped building sailboats in 1980.
http://www.mfggalileo.com/mfg_union_city_history/boat_history/

They also built the Phoenix catamaran.

To answer the question, "Where did all the Dingos go?" - probably the landfill. There weren't very many to begin with and any still around are pushing 40 years old.