Check the SPD Foundation's treatment directory at their Find Services page to locate OTs and other professionals trained in working with children with sensory processing disorder.
A list of EI providers by state is located on the website for the book Raising a Sensory Smart Child.
The site for the American Occupational Therapy Association may be helpful for finding a local occupational therapist trained and experienced in helping children with sensory processing issues.
Western Psychological Services keeps a list of therapists certified to administer the SIPT (Sensory Integration Praxis Test) who may provide services as well.
Check the OT Finder at OT Works in Canada to locate an OT in Canada.