JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Unfortunately it is not possible to populate your dropdown boxes from any external sources.
The only possibility is to download your form's full source code and add your own custom code to fetch and populate the dropdown boxes of your form. The following guide should help you on how to download your form's full source code: http://www.jotform.com/help/104-How-to-get-the-Full-Source-Code-of-your-Form