You don't say where you live, Offgrid, but if you go to
Greek Yellow Pages, type Orthodontists into the What, Who? box and your Prefecture into the "Where?" box you should get a list of Orthodontists in your area. You may be able to narrow the search in the "Where" box as it usually gives a drop down list but I don't think there are very many on the island so I would keep it as wide as possible. Be aware that some of the entries will be in places like Athens and Thessaloniki whatever you put because they have paid to get themselves listed in every search. You could then phone them and ask for estimates.
Warwick