Let me recommend that you go to the website of the U.S. State Department, which updated its section on adoption from Turkey this month. Go to
Intercountry Adoption Turkey.
As you will see, the main issue is not whether Turkey works with agencies. The issue is about how long families have to stay in Turkey when doing an adoption. Under Turkish law, an adoption cannot be finalized until the prospective parents live IN TURKEY for ONE YEAR with the child. And the U.S. government will not issue an immigrant visa to a Turkish child whose adoption has not been finalized according to Turkish law. Since most prospective parents cannot afford to spend a year living in a foreign country, very few ever choose to adopt from Turkey.
Turkey also has some fairly strict age limits for parents, and gives strong preference to Turkish nationals, including people with dual nationality. You can read about these issues on the State Department website.
If you meet the age and other requirements, and if you are willing to spend a year in Turkey, the adoption process is pretty straightforward, based on the State Department information. You should be able to use International Social Services and/or a lawyer to do the adoption.
Sharon