You can contact Robert using the form on this page. There is a "captcha" script (which stands for "Completely Automated Public Turing Test To Tell Computers and Humans Apart") embedded in the form to protect against Web bots that would otherwise abuse the form.
Since Robert is often "in the field" tuning pianos, sending an email is probably the best way to make sure your message reaches him. Nevertheless, use the form of communication that is most convienent.