Hmm, hadn't heard of the term 'equilibrium cranes' till you mentioned it.
Googling brings up 'e-cranes', who I guess you already contacted without much success, and American & Ohio Cranes, who I guess is a distributor for e-cranes . (Unfortunately I could not find a on-line brochure for equilibrium cranes on the brochure menu on that site...
You may have already seen this site, in which case I can't add more information right now, but you are right in that they look interesting...
