which programs require supplemental forms?

Do a search in previous posts for "special requirements" and "application requirements." This has been discussed previously.

Oklahoma and UVa come to mind right away for requiring an additional essay

The best thing to do is to decide what programs you are applying to and then use FREIDA to link to each programs website. All of the websites detail what their application requirements are. It is a bit of a bear to do, but the best way to insure that you meet all of the requirements at each program you apply to. In addition, use other applicants from your home program that are going into ortho as a resource - you can split up the work if you want to. Just my two cents.

Off the top of my head, Washington University, University of Washington, and Yale have supplemental evaluation forms for your LOR writers. A bunch of other programs require a chairman's letter, some others require bizarre things like your MCAT / SAT scores.