Who in Maine can build a tiny house, start to finish?
Tiny house manufacturers work independently of contractors who do the foundation, septic, etc. Is there a reputable eco-conscious company in southeastern Maine that can do it all?
You can find find local tiny house prefab builder in the Ecohome Green Building Professionals Directory, and here you can see models of LEED and Passive House ready prefab kit houses for delivery across Canada and the US, some are modular and to be finished on site, others come fully completed delivered by truck. So it depends on the level of completion you are looking for. Different builders offer different levels of completeness for prefab homes.
Maine requires, for the definition of "tiny house", that models not exceed 400 sq. ft., which I did not find on your site. Did I overlook them?
Yes, there should be more tiny house manufacturers that service your area. in the directory you can search by topic and location. here is a search for green tiny house near me in Maine, another search you could try is prefab ADU accessory dwelling unit near me, which will have overlap in manufacturers so try different search terms. An ADU and tiny house also have overlap, ADU's are often prefab delivered backyard offices that can also be sleeping quarters and even a fully functioning tiny house.
We have come to accept the term 'tiny house' often to mean one that is also mobile, so the difference is often wheels.