If you are near an academic library, you can try searching databases such as Academic Search, which gets 29 hits for the search: attention deficit and adult* and alternative*, 22 of them from scholarly/peer reviewed journals. Psycinfo, a highly technical and scholarly database, gets 64 hits for that same search. For more popular articles, you can search magazine databases such as Masterfile or Infotrac, or newspaper full text databases. Most public libraries allow even remote access to these, with a library card.
You can also search Pubmed, clicking on their "Limits" tab just to lower left of the search box, to choose Adults age group, and even "Links to free full text". Using these limits, I got 11 articles for the search: attention deficit and alternative, 7 for attention deficit and diet, and 10 for attention deficit and nutritional.
Even some highly respected publishers allow free search of their journals - just no free access to full text. For example, Science Direct, a VERY expensive full text database of Elsevier journals, is available at many academic libraries, but also allows anyone to see the titles, authors, and abstracts of most of their articles. The search: "attention deficit" and adult and alternative* gets 16 hits.
For books, it is a bit trickier, because there are limited free full-text or table of contents searches that make it possible to evaluate the books, other than simply by plowing through scattered reviews, and then double-checking the authors of those reviews to judge their merits as reviewers. But for sure you will get some added information in books. Google Books gets 18 hits for the search: "attention deficit" adult "alternative therapy". Even though none of them are full view books, you can copy-paste their titles into a large library's catalog. If you are not near a large library, you can search Open Worldcat to find which libraries anywhere have a particular title. Worldcat lets you "Enter location information" to find libraries nearest to you. You can click on many of those libraries to search their catalogs to find out if the book is actually on the shelf.
